Updated

Barcelona, Aug 18: At least 13 people were killed and more than 100 others injured after drivers slammed into pedestrians in two quick-succession, separate attacks on Barcelona's most popular street and in another busy Spanish seaside city.

Around 4:50 pm local time (1450 GMT) on Thursday, a vehicle ploughed into a crowd of pedestrians on the famous Las Ramblas Boulevard in Barcelona.

The promenade in the heart of the city centre is one of Barcelona's busiest streets, normally thronged with tourists and street performers until well into the night.

Witnesses described scenes of chaos and panic, with bodies strewn along the boulevard as others fled for their lives.

"When it happened I ran out and saw the damage," local shop worker Xavi Perez said.

"There were bodies on the ground with people crowding round them. People were crying. There were lots of foreigners."

Some eight hours later in Cambrils, a city 120 kilometres south of Barcelona, an Audi A3 car hit pedestrians, injuring six civilians -- one of them in a critical condition -- and a police officer.

Police shot four of the attackers dead and fifth later died of his injuries, saying they were "working on the hypothesis that the terrorists shot dead in Cambrils are linked to what happened in Barcelona".

Little more was known about this second attack early on Friday morning.

Regional interior minister Joaquim Forn said at least 13 people had died and around 100 more were injured in the Barcelona attack.

There were at least 18 nationalities among the Barcelona victims who came from countries as varied as France, Venezuela, Australia, Ireland, Peru, Algeria and China, according to Spain's civil protection agency.

Belgium said one of its citizens had died, while The Hague said three Dutch were injured and a Greek diplomat reported three nationals had been wounded -- a woman and her two children.

Police in the Spanish region of Catalonia where both cities are located said they have arrested two men, a Spaniard and a Moroccan, but the driver of the van is still on the run.

Police are treating the Barcelona incident as a "terrorist attack" but have not commented officially on the Cambrils rampage.

One of the suspects arrested over the Barcelona attack is a man born in the Spanish territory of Melilla in northern Morocco.

The other who has been named, Driss Oukabir, is Moroccan.

The Islamic State's propaganda agency Amaq claimed that "soldiers" from the jihadist group carried out the attack, according to the SITE Intelligence Group which monitors Islamist websites.

"The executors of the Barcelona attack were soldiers of the Islamic State," the Amaq outlet said, quoted by SITE.

Separately, police said they suspected a house explosion late Wednesday at a house in Alcanar some 200 kilometres (124 miles) south of Barcelona was linked to the van attack. At least one person died in the house where police suspect they were "preparing an explosive device".

Emergency services quickly arrived on the scene and cordoned off the area, with several ambulances and police vehicles responding.

The city also closed down metro stations in the area, with authorities telling people to stay away from the area.

Prime Minister Mariano Rajoy tweeted that he was in contact with the local authorities, saying the priority was to help the victims and facilitate the work of security forces.

Police appealed to people to stay in their homes and avoid unnecessary trips.

Spain was hit by what is still Europe's deadliest jihadist attack in March 2004, when bombs exploded on commuter trains in Madrid, killing 191 people in an attack claimed by al-Qaeda-inspired extremists.

In July 2015, a hooded attacker opened fire outside a hotel in downtown Barcelona near Las Ramblas boulevard, leaving two people injured, police said. No suspected motive for that attack was given.

Earlier Report

13 dead as van crashes into crowd in Barcelona terror attack

Barcelona, Aug 17 (Agencies): Thirteen people were killed after a white van crashed into pedestrians at the city centre in Barcelona on Thursday, Cadena SER Radio said, citing police sources.

Spain's El Periodico newspaper also said between 20 to 25 people were injured as a van mowed down pedestrians on Las Ramblas, a spot popular with tourists in Barcelona, citing police sources.

Soon afterwards, El Periodico reported that two armed men were holed up in a bar in Barcelona's city centre, and said that there was gunfire in the area, although it did not cite the source of the information.

It was, however, not clear whether the incidents were connected.

After the van crash, Spanish Prime Minister Mariano Rajoy said he is in contact with all the authorities, priority is to attend to the injured.

Catalan Police said they have activated protocols for the attack but cannot confirm motive behind the crash.

In a photograph shown by public broadcaster RTVE, three people were lying on the ground in the street of the northern Spanish city this afternoon, apparently being helped by police and others.

Police in Barcelona, Spain's second-largest city, told crowds fleeing the scene by megaphone that they were dealing with a "terrorist attack".

Videos of the scene recorded people screaming as they fled.

Police cordoned off the broad, popular street, ordering stores and nearby Metro and train stations to close.

They asked people to stay away from the area so as not to get in the way of emergency services. A helicopter hovered over the scene.

Train and metro stations were closed in the area, according to local newspaper La Vanguardia.

Las Ramblas, a street of stalls and shops that cuts through the center of Barcelona, is one of the city's top tourist destinations. People walk down a wide, pedestrianized path in the center of the street, but cars can travel on either side.

Initially, police described the incident on Twitter as a "massive crash". Emergency services said people should not go to the area around the city's Placa Catalunya, and requested the closure of nearby train and metro stations.

El Pais newspaper said the driver of the vehicle had fled on foot after mowing down dozens of people.

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.

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.