A van ploughed into crowds in the heart of Barcelona on Thursday and Spanish media reported at least 13 people were killed, in what police said they were treating as a terrorist attack.

Regional authorities said one death had been confirmed so far, with 32 injured, 10 seriously. But radio station Cadena Ser cited police sources as saying the death toll was much higher.

Police said they said were searching for the driver of the van who, according to local media, fled the scene on foot.

Injured people are treated in Barcelona, Spain, Thursday, August 17, 2017. Photo: AP

Spanish newspaper El Periodico said two armed men were holed up in a bar in Barcelona's city centre, and reported gunfire in the area, though it did not cite the source of the information.

It was not immediately clear whether the incidents were connected.

Second van linked to the attack found in town of Vic

Meanwhile, a second van linked to the attack has been found in the small town of Vic in Catalonia, local authorities there said on Twitter.

Police had cordoned off the area and were inspecting the vehicle, the city council said.

Spanish media earlier reported that a second van had been rented as a getaway car by attackers.

A source familiar with the initial U.S. government assessment said the incident appeared to be terrorism, and a White House spokeswoman said President Donald Trump was being kept abreast of the situation.

Children, some in tears, are escorted down a road in Barcelona, Spain, Thursday, Aug. 17, 2017. Photo: AP

Media reports said the van had zigzagged at speed down the famous Las Ramblas avenue, a magnet for tourists.

"I heard screams and a bit of a crash and then I just saw the crowd parting and this van going full pelt down the middle of the Ramblas and I immediately knew that it was a terrorist attack or something like that," eyewitness Tom Gueller told the BBC.

An injured person is treated in Barcelona, Spain, Thursday, August 17, 2017. Photo: AP

"It wasn't slowing down at all. It was just going straight through the middle of the crowds in the middle of the Ramblas."

Mobile phone footage posted on Twitter showed several bodies strewn along the Ramblas, some motionless. Paramedics and bystanders bent over them, treating them and trying to comfort those still conscious.

Around them, the boulevard was deserted, covered in rubbish and abandoned objects including hats, flip-flops, bags and a pram.

"We saw a white van collide with people. We saw people going flying because of the collision, we also saw three cyclists go flying," Ellen Vercamm, on holiday in Barcelona, told El Pais newspaper.

TOURIST DRAW

Emergency services said people should not go to the area around Barcelona's Placa Catalunya, one of the city's main squares at the top of the Ramblas, and requested the closure of nearby train and metro stations.

Prime Minister Mariano Rajoy said he was in contact with authorities, and the priority was to attend to the injured.

The incident took place at the height of the tourist season in Barcelona, which is one of Europe's top travel destinations with at least 11 million visitors a year.

Vehicles have been used to ram into crowds in a series of militant attacks across Europe since July 2016, killing well over 100 people in Nice, Berlin, London and Stockholm.

Witness Ethan Spibey told Britain's Sky News: "All of sudden it was real chaos. People just started running screaming, there were loud bangs. People just started running into shops, there was a kind of mini-stampede where we were, down one of the alleyways."

He said he had taken refuge with dozens of other people in a nearby church.

"They've locked the doors because I'm not sure whether the person who may have done it has actually been caught, so they've locked the doors and told people just to wait in here."

Authorities in Vic, a small town outside Barcelona, said a van had been found there in connection with the attack. Spanish media had earlier reported that a second van had been hired as a getaway vehicle.

Barcelona is the capital of the wealthy northeastern region of Catalonia, which plans to hold a popular vote on Oct. 1 on whether it should secede from Spain. It is in dispute with the central government, which says the vote cannot go ahead because it is unconstitutional.

If Spanish media reports of at least 13 killed are confirmed, it would be the deadliest in Spain since March 2004, when Islamist militants placed bombs on commuter trains in Madrid, killing 191 people and wounding more than 1,800.