Britain's parliament reopened Thursday with a minute's silence in memory of three people killed in a suspected "Islamist-related" attack on the symbol of the country's democracy.
With MPs projecting an air of "business as usual," armed police arrested eight people in raids linked to Wednesday's deadly assault carried out in the shadow of Big Ben that sowed panic in the heart of London.
Around 30 people were treated in hospital, including seven in critical condition, some with "catastrophic" injuries after the attacker mowed down pedestrians on a nearby bridge before stabbing a policeman at the parliament gates.
As MPs resumed business, police officers lined up outside their Scotland Yard headquarters nearby for a minute's silence in front of the eternal flame to those officers who have given their lives in service.
A packed parliament paid tribute, heads bowed.
"We are not afraid and our resolve will never waver in the face of terrorism," said a defiant Prime Minister Theresa May.
Britain had until Wednesday's attack been spared amid a series of deadly jihadist assaults in Europe.
The attack in London came a year to the day after Islamic State jihadists killed 32 people in twin bomb attacks in Brussels.
Attacker 'acted alone'
Britain's top anti-terror officer Mark Rowley said police had raided six houses in London, the central city of Birmingham and elsewhere.
"It is still our belief... that this attacker acted alone yesterday and was inspired by international terrorism," he said.
Rowley acknowledged Muslim communities "will feel anxious at this time" due to previous extreme right-wing attacks and that the police would work with community leaders to ensure protection.
One of those killed was Aysha Frade, who worked in the administration team at a school a few hundred metres away.
Among the injured were three French school children and a number of foreign nationals from China, Portugal, Romania and South Korea.
'Sick and depraved'
At the scene of the attack, helicopters circled overhead and a blue forensics tent was in place where the assailant died. Where the policeman was killed, there was blood on the ground.
Hundreds of extra police were on patrol as officers worked around the clock to piece together what happened in the deadliest attack in Britain since four suicide bombers killed 52 people on London's transport system in July 2005.
The British flag over parliament flew at half-mast in a sign of mourning.
Press Association news agency photos believed to be of the knifeman lying on an ambulance stretcher showed a burly man with black clothes and a beard.
Other pictures showed a knife on the cobblestones inside the vehicle entrance gates to parliament, while three shots were heard ringing out on video footage as terrified passers-by fled.
Standing outside her Downing Street residence after an emergency cabinet meeting on Wednesday, May said Britain's alert level would remain unchanged at level four, or "severe".
The prime minister was in parliament at the time of the attack and was ushered away in a silver car as gunfire rang out.
Foreign Office minister Tobias Ellwood, whose brother Jonathan was killed in the 2002 Bali bombing, was pictured with his face smeared with blood helping to give first aid to the fatally wounded police officer.
Candlelit vigil
Queen Elizabeth II postponed her appearance on Thursday to open the new headquarters of London's Metropolitan Police and London's mayor Sadiq Khan called a candlelit vigil on Trafalgar Square later in the day.
Britain's allies vowed to stand with London in the fight against terror while lights on the Eiffel Tower in Paris were switched off at midnight in solidarity with the victims.
US President Donald Trump and French President Francois Hollande both spoke to May and Chancellor Angela Merkel said Germany stood with Britons "against all forms of terrorism".
Britain's last terror attack was last year's assassination of MP Jo Cox by a pro-Nazi sympathiser in her constituency in northern England shortly before the vote to leave the European Union.
International victims
Several international tourists visiting one of London's most iconic sights were caught up in the violence.
French Foreign Minister Jean-Marc Ayrault travelled to London to visit three French pupils on a school trip who were among those hurt.
Five South Korean tourists were wounded, Seoul's foreign ministry said, while the Romanian government said two of its citizens were also injured.
A Portuguese man was hurt, the country's government said, while a seriously injured woman was rescued from the River Thames following the incident.
A Chinese tourist was also slightly injured.
The victims
Three people were killed in the London terror attack outside the Houses of Parliament -- two members of the public and a police officer.
Police said 40 were injured after the attacker ploughed a car along a pavement on a bridge before stabbing the police officer outside the parliament.
Here is what we know about the victims so far.
A minute's silence is observed outside New Scotland Yard in London to pay respect to the victims of terror attack. Source: AAP
Police officer
The police officer killed has been named as 48-year-old Keith Palmer, a husband and father who was part of the parliamentary protection force.
Tributes have poured in from across the country for Palmer, who was unarmed and was stabbed to death just inside the vehicle entrance gates to parliament.
Palmer had been in the police for 15 years.
He previously served in the British army alongside James Cleverly, now a Conservative MP, who tweeted: "A lovely man, a friend. I'm heartbroken."
Female pedestrian
British police said one of the victims run down and killed by the attacker was a woman in her mid-40s.
According to a Spanish diplomatic source, she had a Spanish mother but was a British citizen.
Media reports said she was a 43 year-old mother of two and taught Spanish in London.
In the hours after the attack sowed confusion on heavily-trafficked Westminster Bridge, Colleen Anderson, a junior doctor at the nearby St Thomas' Hospital, said she had confirmed the death of a woman at the scene.
"She was under the wheel of a bus," she said, without explaining how the victim came to be under the bus.
Male pedestrian
British police said the third victim was a man in his mid-50s but provided no further details.
Injured
Westminster Bridge is a busy tourist spot with its views of parliament's Big Ben clock tower, and the injured included several foreigners.
Police said 29 of around 40 people wounded were treated in hospital. Seven remained in a "critical condition" on Thursday.
Three French pupils on a school trip to London were among those hurt, including two who suffered broken bones but were not reported to be in life-threatening condition.
The teenagers are from a high school in Concarneau, in the western Brittany region, and were joined by their families on Wednesday evening.
Five South Korean tourists -- four women and a man in their 50s and 60s -- were also wounded after being knocked to the ground by people trying to flee as the assailant mowed down pedestrians in a car, Seoul's foreign ministry said.
A woman with serious injuries was rescued from the River Thames near Westminster Bridge after the attack. No mention was made of her name or nationality.
Other casualties include a Portuguese man, a Chinese person and two Romanians, authorities in their respective countries confirmed.
