18/08/2017 11:13 AM AEST | Updated 18/08/2017 2:36 PM AEST

Barcelona Terror: Manhunt Underway For Driver As Police Foil Second Terror Attack

Police say they killed four people in response to a second terror plot.

Spanish police have killed several people in response a second suspected terror plot in Spain, as an intense man-hunt gets underway for a driver who killed up to 16 people when he plowed through pedestrians at a popular tourist thoroughfare in Barcelona.

More than 100 people, including two New South Wales women and two men form Victoria, were injured in the Barcelona attack, while Catalonia President Carles Puigdemont said two suspects were arrested. An manhunt is underway for the driver of the van, however, who was still at large as of 11pm local time.

Just hours later, Spanish police said they had killed five people in response to a separate terrorist plot in the southern coastal town of Cambrils, about 100 kilometres southwest of Barcelona. The injured man has been detained by police.

Key points:

Police said six bystanders and one police officer were injured in Cambrils. There are reports police feared the suspects were planning to drive a van into pedestrians on the coastal town's popular seaside strip.

The first attack, in popular tourist spot Las Ramblas, left dozens of people bloody in the streets and prompted others to run from the area, terrified for their lives, when a van plowed into the crowd.

The van "was weaving left and right, trying to hit people as fast as possible", a witness told the BBC.

JOSEP LAGO via Getty Images
A driver deliberately rammed a van into a crowd on Barcelona's most popular street on August 17, 2017 killing at least 13 people before fleeing to a nearby bar, police said.

The self-described Islamic State claimed responsibility for the attack via its Amaq news agency. However, it is unclear to what extent, if any, the group's leadership was directly involved.

Bishop said that the Australian Government was "determined to take part in the international effort to combat and defeat terrorists wherever they may be", urging Australians to continue going about their "normal lives".

"Tragically, terrorist attacks are taking place around the world," she said.

"No one country, no one city is immune."

The attack occurred on Las Ramblas, a historic street leading to a central plaza in Barcelona. A pedestrian walkway runs down the center of the street, with cars driving on either side.

"There was loud bangs and people started running into shops," witness Ethan Spibey told Sky News, describing a "mini stampede" of people running down an alleyway.

JOSEP LAGO via Getty Images
Policemen check the area after towing away the van which ploughed into the crowd, killing at least 13 people and injuring around 100 others on the Rambla in Barcelona, on August 18, 2017. A driver deliberately rammed a van into a crowd on Barcelona's most popular street on August 17, 2017 killing at least 13 people before fleeing to a nearby bar, police said. Officers in Spain's second-largest city said the ramming on Las Ramblas was a 'terrorist attack'. The driver of a van that mowed into a packed street in Barcelona is still on the run, Spanish police said. / AFP PHOTO / Josep LAGO (Photo credit should read JOSEP LAGO/AFP/Getty Images)

Melbourne woman Alana Reader locked in a retail store when the Barcelona attack happened.

"We were locked in the store, confused at first at what was going on and then all of a sudden we saw people running and screaming with genuine fear," she wrote on Facebook.

"We spent about 20 minutes after that lying down on the floor, with an Israeli family, British family and German girl.

"I've never been so terrified, it's a feeling I'll never be able to describe and hope I never experience again but so grateful I'm alive and here in beautiful Barcelona."

Authorities immediately locked down the area, shutting metro stations and asking businesses to close.

A first responder to Melbourne's deadly Bourke Street massacre said the attack in Barcelona was "a little bit too close to home" and "very similar".

Metropolitan Fire Brigade (MFB) Commander Graeme O'Sullivan told 3AW that he and his wife were on the roof terrace of their hotel in Barcelona when they "heard a loud rumbling sound" followed by "thud sounds".

"That was the vehicle running into two pedestrians and then a short time after that screams," he said.

"It was pretty clear to us it was another one of these incidents -- a deliberate act."

Meanwhile an explosion at a house 200 kilometres south of Barcelona on Wednesday night is now being linked by police to the Barcelona terrorist attack.

Police had initially dismissed the explosion in Alcanar as a gas explosion.

But Catalonia police on Friday said they were now linking the two.

"We work with the hypothesis that the downed terrorists would be related to the events recorded in Barcelona and Alcanar," they said.

They said they were working to determine if the alleged terrorists in Cambrils were using explosive belts.

"In few minutes we are going to make several controlled explosions in Cambrils. If you hear detonations do not be alarmed, are controlled."

Australian Governor General Peter Cosgrove said he will meet with the Spanish ambassador.

"Yet again, an evil individual slaughtered the innocent," he said.

The Department of Foreign Affairs and Trade (DFAT) has said that Australians concerned about family or friends in the region should contact them directly before calling the 24-hour Consular Emergency Centre on 1 300 555 135 (+61 2 6261 3305 if calling from overseas).