30/03/2017 7:48 AM AEDT | Updated 31/03/2017 12:21 AM AEDT

Ex-Cyclone Debbie Now Causing Havoc In Queensland and Northern NSW

It's going to be a long night for a lot of people around the border region.

Flood levels are continuing to rise dramatically in large parts of the south-eastern Queensland and north-east NSW regions.

Following a day of unprecedented rains and destructive winds, evacuation orders were given to up to 40,000 residents in the South Murwillumbah, Condong, Tumbulgum, Lismore, Chinderah, Kingscliff, Fingal Head and Bilambil areas.

Over 400mm of rain had fallen in the past 24 hours and authorities were expecting at least another 200mm to fall overnight on Thursday.

NSW Police ordered for Lismore residents to be evacuated around 5pm local time as the Wilsons River was expected to reach its peak of 11 metres in the early hours of Friday morning.

NSW SES has also issued a flood watch warning for residents in the surrounding areas of the Richmond-Wilsons River Valley, which has the potential for flash flooding to develop throughout the night.

Acting Deputy Commissioner of the NSW SES Mark Morrow said: "We have an order in place for south Murwillumbah, Condong and Tumbulgum on the upper Tweed catchment.

"On the lower part that evacuation order relates to parts of Tweed Heads to the south and west, Kingscliff, Chinderah, Fingal Head and the main evacuation order we're dealing with at the moment relates to the Lismore CBD."

By 7pm (AEDT), NSW police had been forced to attend to 35 flood rescues across northern NSW after receiving up to 700 requests for assistance. They reiterated their calls for people to act responsibly and have confirmed the chance further evacuations in other suburbs on Thursday night is high.

Morrow also said evacuation centres have been opened in Lismore, Murwillumbah and Kingscliff, among other locations listed on the SES website, for those who are affected.

The full list of NSW flood warnings and orders are here at the SES website. Numerous alerts are in place for the Gold Coast and other south-east Queensland localities. You can see the warnings and orders at the Queensland SES site here.

Jason O'Brien via Getty Images
Floodwaters have reached north-eastern NSW in the wake of Cyclone Debbie.

Meanwhile schools in south-east Queensland will remain shut on Friday and people are urged to remain indoors amid flash flooding that reached Brisbane on Thursday afternoon.

Queensland Premier Annastacia Palaszczuk said the decision to extend the closures comes in order to protect the safety of families and children in affected areas while the "severe weather system" continues moving towards the south-east.

"This severe weather system that started with Cyclone Debbie and is tracking down the coast is causing havoc across our state," she said.

"We have not seen the worst of this severe weather system in the south-east of our state, we are going to see heavy rainfalls, we are going to see thunder. This is a severe weather event.

"I apologise for any inconvenience but I do not apologise for putting the safety of Queenslanders, families and children front and centre. That is why the schools will remain closed tomorrow."

Deputy Premier Jackie Trad announced just after 8am on Thursday morning that all schools in south-east Queensland were closed, including schools from Agnes Waters to the New South Wales border as far inland as Nanango, encompassing Brisbane, the Sunshine Coast and Bundaberg.

Parts of Brisbane were underwater as of lunchtime Thursday, after more than 200mm of rain fell between midnight and midday on Thursday, with Springbrook on the Gold Coast receiving around 380mm.

No further serious injuries or losses of life have been recorded, according to the Queensland Police.

At 7:30pm on Thursday night, Queensland Fire and Emergency and SES had confirmed it has received more than 4000 calls for assistance since Cyclone Debbie hit land on Tuesday.

People were queueing for up to an hour for sandbags to project their homes at Brisbane depos, with council workers making 4,000 sandbags an hour to keep up with demand.

Meanwhile northern Queensland has continued to experience flash flooding overnight, with the region west of Mackay worst affected.

Around 50 people were still trapped in floodwaters near the cyclone-ravaged town on Thursday.

Heavy rainfall from 9pm on Wednesday night saw people trapped in submerged cars and on rooftops, with 38 water rescue incidents taking place overnight.

A further 11 people in Eton and 40 in the Homebush area just outside of Mackay were still awaiting rescue on Thursday morning, Queensland Fire and Emergency Services Commissioner Katarina Carroll confirmed.

Carroll said that rescue helicopters had been able to reach the area early on Thursday morning and 12 rescues were currently underway.

"Please be patient with us, we will get to you as soon as humanly possible," she said.

A heavily pregnant woman was evacuated from a house in Homebush early on Thursday and taken to the Eton rural fire shed, the QFES Commissioner said, adding she has since been taken by helicopter to West Leagues Club.

Dangerous conditions reached south-east Queensland on Thursday morning, with people in low-lying areas being urged to go and stay with relatives and friends.

Tony Moore / Fairfax Media
Stormwater drains overflow and flood streets as the downpour reaches Brisbane.

"This sting in the tail of Debbie is something we knew would happen," Commissioner of Police Ian Stewart said.

"We knew it would turn into a low, but it's turned into a very severe weather event in itself. Those levels of rain are something we probably haven't seen in a number of years."

Bureau of Meteorology
A large area of south-east Queensland is on Flood Watch.

Palaszczuk was also summoned back to Brisbane from northern Queensland -- where she was assisting the recovery efforts in towns ravaged by Cyclone Debbie -- to deal with the new threat.

The deluge is expected to worsen into the afternoon, leading to police urging business owners to send employers home early to avoid the worst of the flash floods, with possible public transport closures flagged.

All non-essential public servants have been sent home across south-east Queensland, and public transport has been made free from 10am on Thursday to allow people to get home safely.

People in flood-affected areas are being warned not to drive through floodwaters and to stay indoors unless absolutely necessary. There were widespread road closures across south-east Queensland, including sections of the Bruce Highway north of Brisbane.

Brisbane Airport remained open as of 12:30pm Thursday, but some flights had been cancelled.

Much further south, Sydney has received moderate rain on Thursday, but it is the winds which pose the greatest threat to Sydneysiders.

"Damaging winds averaging 65km/h with gusts in excess of 90km/h are possible along the coastal fringe from about Sydney to Forster during Thursday afternoon and evening, then extending to the remainder of the northern coastal fringe during Friday," the Bureau said in a statement.

While not in the range of the cyclonic conditions of up to 263km/h seen in northern Queensland on Tuesday, it is still enough to blow branches from trees and create dangerous conditions on the road.

Meanwhile, relief is arriving for some of the islands worst affected by Cyclone Debbie.

People will finally be able to leave Hamilton Island, where they have been trapped by strong winds and wild seas since Cyclone Debbie devastated the tourist hotspot on Tuesday. Eleven flights are scheduled in and out of the island today, after flights had to be cancelled on Wednesday evening due to ongoing wild weather.

We knew it would turn into a low, but it's turn into a very severe weather event in itself. Those levels of rain are something we probably haven't seen in a number of years."

Around 200 tourists and 100 staff trapped on the tiny Daydream Island without running water since Tuesday will also be able to leave, with ferry services to the island expected to be back up and running today.

Malcolm Turnbull and Bill Shorten have been visiting the cyclone-ravaged communities of northern Queensland.

In a joint press conference on Thursday morning, they urged holidaymakers not to abandon the region, which relies heavily on tourism to support its economy.

"They will have to work very hard to get back on their feet, and they will get back on their feet," Bill Shorten said. "I think the best way the rest of Australia can help is to think about the Whitsunday region for your next holiday."

This is a developing story.