"Soldiers of the Islamic State were acting on command of caliph," the ISIS media channel Amaq agency said.

Around 5pm local time, a vehicle slammed into a crowd of pedestrians on the famous Las Ramblas boulevard. Witnesses described scenes of chaos and panic as they tried to flee. The Las Ramblas boulevard is one of Barcelona's busiest streets. Street performers and tourists throng the area well into the night.

The Spanish police called the incident a terror attack minutes after it happened. The police have cordoned off the area and shut sown public transport, including the metro services, in the area.

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

There is no report of any Indian casualty in the Barcelona terror attack, External Affairs Minister Sushma Swaraj said.

The United States offered assistance to Spain. "The United States condemns the terror attack in Barcelona, Spain, and will do whatever is necessary to help. Be tough & strong, we love you!" tweeted US President Donald Trump.

Since July 2016, vehicles have been used to plough into crowds in a series of terror attacks across Europe, killing well over 100 people in Nice, Berlin, London and Stockholm.

In recent weeks, threatening graffiti against tourists has appeared in Barcelona, which draws at least 11 million visitors a year. In one video released under the slogan "tourism kills neighbourhoods", several hooded individuals stopped a tourist bus in Barcelona, slashed the tyres and spray-painted the windscreen.

Spain was hit by what is still Europe's deadliest terror strike in March 2004, when bombs exploded on commuter trains in Madrid, killing 191 people. Al Qaeda-inspired extremists claimed responsibility for the attack.