This is for Allah: Eyewitnesses heard London attackers on stabbing spree say

London: Three assailants stabbed passers-by at random after smashing into pedestrians in a van, killing six people in a "terror attack" in a popular night-life hub in London before armed police shot all three dead.

As they rampaged through the bars around London Bridge on Saturday night, the trio wore what looked like suicide vests which turned out to be "hoaxes", said Mark Rowley, head of counter-terrorism policing.

"We believe that six people have died in addition to the three attackers shot dead by police" in what is being treated as a "terrorist incident", Rowley said.

Some 48 casualties were rushed to hospitals in the area, according to the London Ambulance Service.

The injured included a British Transport Police officer who was one of the first responders on the scene and was stabbed in the face and leg.

The attack came just five days ahead of a general election and only minutes after the end of the Champions League final between Real Madrid and Juventus, in an area teeming with bars where many fans were watching the football on television.

"They were stabbing everyone. They were running up and going 'This is for Allah'," a man called Gerard told the BBC, adding that he had seen the assailants stabbing a girl and had tried to confront them.

Another witness called Eric told the BBC he had seen three men come out of the white van after hitting pedestrians and thought they were going to help.

But instead they "started kicking them, punching them and took out knives. It was a rampage really," he said, adding that he also heard a shout of: "This is for Allah".

Britain is on high alert only 12 days after a suicide bomber killed 22 people at a concert in Manchester, northwest England and ahead of Thursday's general election, in which security is a major theme.

It is the latest in a string of attacks to hit Europe, including in Paris, Berlin and Saint Petersburg.

Facebook activated its safety check function for people in London to let their loved ones know they are safe and local residents offered accommodation for anyone left stranded by the attack, under the hashtag #sofaforlondon.

Witnesses described the van speeding into several pedestrians on London Bridge and then the knife-wielding men sprinting towards bars packed with revellers enjoying a Saturday night out.

Several people said they were ordered to stay inside pubs and restaurants by police and eventually had to come out with their hands on their heads.

Italian photographer Gabriele Sciotto, who was watching the football at the Wheatsheaf pub in Borough Market, said he saw three men shot just outside the pub.

In his picture, a man wearing combat trousers, with a shaved head and what looked like a belt with canisters attached to it could be seen on the ground with two more bodies behind him.

"In two or five seconds, they shot all the three men down," Sciotto told the BBC.

Police said the three men were shot by a police armed response team within eight minutes of receiving the first call at 10:08 pm British time (2108 GMT).

Dozens of emergency vehicles could be seen and a wide area around London Bridge was cordoned off as two helicopters hovered overhead. Media reports said there were three controlled explosions carried out by police during the night.

The attack had harrowing echoes of the one on London's Westminster Bridge when British Muslim convert Khalid Masood rammed his car into pedestrians before crashing into the barriers surrounding parliament and then stabbing a police officer to death.

Masood was shot dead by a ministerial bodyguard.

Prime Minister Theresa May, who is due to hold an emergency cabinet meeting on Sunday, confirmed the "terrible incident in London" was being treated as "a potential act of terrorism."

"Our thoughts are with those who caught up in these dreadful events," she said in a statement.

US President Donald Trump offered his help, tweeting "WE ARE WITH YOU. GOD BLESS!"

Trump also seized the occasion to plug his thwarted ban on travellers from six mainly Muslim countries.

French President Emmanuel Macron meanwhile said France was "more than ever at Britain's side."

US pop star Ariana Grande, whose concert in Manchester was the scene of last week's fatal terror attack, tweeted: "Praying for London".

Witnesses on London Bridge reported seeing a van mounting the pavement and hitting pedestrians.

"There was a van that crashed into the fences on London Bridge. And then there was a man with a knife, he was running. He came down the stairs and went to the bar," Dee, 26, who was visibly in shock and declined to give her last name, said.

Alex Shellum at the Mudlark pub near the scene of the attack said a woman had come into the bar "bleeding heavily from the neck".

"It appeared that her throat had been cut," he told the BBC.

Husband and wife Ben and Natalie told BBC radio they were outside Borough Market when they witnessed a stabbing.

Ben said: "We saw people running away and then I saw a man in red with a large blade, at a guess 10 inches (25 centimetres) long, stabbing a man, about three times".