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At least 13 people were killed and more than 50 injured after a van rammed through crowds of people in the heart of Barcelona on Thursday in an apparent terror attack.

Eyewitnesses reported panic and chaos as the van plowed through crowds in the renowned Las Ramblas avenue, which was teeming at the time with locals and tourists.

One person has been arrested, Catalan police said. Police are treating the incident as a terror attack and have sealed off the area.

“We can confirm 13 dead and more than 50 injured,” Joaquim Forn, the Catalan interior minister, told a news conference.

He had earlier given initial figures of one dead and 32 injured but warned the toll was “bound to rise.”

City officials ordered all public events to be canceled, while emergency services requested the closure of metro and train stations in the area.

Reports of the attack first emerged on social media at about 5 p.m. local time (11 a.m. ET). About two hours later, police confirmed Spain had suffered a deadly attack.

It was the latest in a series of attacks in Europe in which vehicles have been used to mow down pedestrians in public spaces.

Catalan police said they were continuing to hunt for the perpetrators and the force had activated its terror response protocols. Unconfirmed reports suggested the suspects may have been attempting to reach a getaway vehicle.

Local Spanish media earlier reported two armed men had entered a restaurant.

As the incident unfolded, police told everyone in the vicinity of Plaça de Catalunya and Las Ramblas to remain indoors until told it was safe to go outside. Footage posted to social media by witnesses showed chaotic scenes with people lying in the street, apparently dead or injured.

The Islamic State group has claimed responsibility for the van attack.

A statement carried by the extremist group’s media arm, the Aamaq news agency, says Thursday’s attack was carried out by “soldiers of the Islamic State.”

It says the attack was in response to IS calls for its followers to target countries participating in the coalition trying to drive the extremist group from Syria and Iraq.

The statement provided no further details about the attackers.

Witness reports gunshots

One witness told local media the situation was “very tense” and all surrounding shops were being evacuated. The witness said at least eight ambulances were at the scene. Emergency services said the area had been cordoned off and all public transportation stopped.

Another witness who was hiding in a shop nearby heard gunshots, according to state-run broadcaster TVE24.

Another witness said he saw a van driving “around 80 kilometers” per hour, or 50 mph. He said “there is no doubt it was intentional,” according to TVE24.

Tourist Susan McClean told CNN she saw a “tidal wave” of people running away from Las Ramblas in the aftermath of the incident.

She ducked into a nearby shop, and the shutters were pulled down while police sped toward the scene.

“There was clearly a lot of distress,” she told CNN.

McClean said she returned to her hotel just a street away after leaving the shop.

Witness: “Lot of distress”

The Catalonian regional government is convening an emergency meeting to discuss the incident, said its vice-president, Oriol Junqueras, in a tweet.

The Catalan emergency services urged people via Twitter to avoid going out or undertaking any other type of movement that is not “strictly necessary” to facilitate police operations.

Spanish Prime Minister Mariano Rajoy tweeted: “In contact with all administrations. Priority: tend to the injured in Las Ramblas and facilitate the work of security forces.”

NATO Secretary General Jens Stoltenberg tweeted his condemnation of the attack.

“My thoughts are with all those affected. We stand united in the fight against terrorism,” he said.

London Mayor Sadiq Khan also tweeted his support, saying: “London stands with Barcelona against the evil of terrorism.”

The US Consulate in Barcelona posted on Twitter: “We are aware of a reported incident at Las Ramblas in Barcelona. Please avoid the area and monitor local police @mossos for updates.”

Las Ramblas is a predominantly pedestrianized street popular among tourists in Barcelona. Extending for about three-quarters of a mile through the center of the city, the tree-lined street is especially crowded in the summer, the height of tourist season.

The promenade passes by kiosks, flower sellers, pavement cafes and bars. It includes a number of the city’s most popular sites.

Barcelona is consistently ranked one of the world’s most visited cities.

Facebook has activated its Safety Check feature for Barcelona.