Spanish authorities have confirmed that at least 13 people have died and 100 have been injured in a terrorist attack in the heart of Barcelona, after a van drove into a crowd of pedestrians in the Las Ramblas area.

The driver is believed to be at large. Two arrests have been made and the suspects are being treated as terrorists.

Authorities say the vehicle mounted a pavement and struck several people in a "massive crash" in the popular tourist area.

Extremist group Isis has claimed responsibilty for the attack, which has also been linked to an earlier house explosion in the city of Alcanar, 120 miles south of Barcelona.

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La Vanguardia newspaper reported that the van entered the pedestrian street from Placa de Catalunya and crashed into the second kiosk on La Rambla.

Daniela Goicoechea, who was walking along La Rambla with three children aged one, two and five, told the Independent: "People started running but we didn't know what was happening. There was a lot of people running. Then policemen began chasing people. We were lost, we ran with three babies and hid in a cafe nearby."

Pictures of the van show a white vehicle with the logo of the rental company Telefurgo on its side.

While full details of the incident were not immediately clear, since July 2016 vehicles have been used to ram into crowds in a series of militant attacks across Europe, killing well over 100 people in Nice, Berlin, London and Stockholm.