4 including cop killed in British parliament attack

Four people have been killed, including the stabbed officer and a male terrorist, and at least 20 injured in an attack on the Houses of Parliament Wednesday afternoon in a terrorist attack, police announced.

Metz Police Assistant Commissioner Mark Rowley confirmed the deaths in a briefing at New Scotland Yard.

The police officer died after being stabbed outside the House of Parliament. Several others are critically injured after a vehicle ploughed into crowd on Westminster Bridge just outside the Parliament.

Mark Rowley, the national lead for Counter Terrorism Policing and the Acting Deputy Commissioner said in a statement that the attack started when a car was driven over Westminster Bridge, hitting and injuring a number of people and three police officers.

"The car then crashed near to Parliament and at least one man, armed with a knife, continued the attack, trying to enter Parliament," said the statement.

The terrorist who stabbed the police officer was shot by police officers who raced to aid their colleagues.

The terrorist was taken to hospital and died.

The injured officers was also rushed to hospital for emergency treatment.

Hospital authorities in London said at least 10 people were being treated.

London Ambulance said an injured woman was pulled alive from the River Thames.

Among the injured, three are French students, who were on a school trip in London when the attack happened, French foreign ministry confirmed.

As the incident continued, hundreds of people fled from the scene, fearing a bomb attack on Westminster.

Business in the Houses of Parliament was immediately suspended, with around 500 politicians, staff and visitors moved to a safe area as the building was placed in a security lockdown. Specially trained officers were combing the parliament buildings for bombs or explosives.

Downing Street issued a statement saying Prime Minister Theresa May was safe after security police whisked her from the Houses of Parliament to 10 Downing Street.

May was planning to hold a special meeting later Wednesday of Britain's main security advisors, known as the Cobra committee.

The London Eye, one of the capital's biggest tourist attractions, was shut down, leaving many people spending several hours in the pods high above the River Thames.

Commander BJ Harrington of the Metropolitan Police said a major terrorist incident had been declared.

"Although we remain open minded to the motive, a full terrorism investigation is underway led by the Met's Counter Terrorism Command," said Harrington.

Media in London reported that Foreign Office government minister Tobias Ellwood, a former captain in the British military, ran to the aid of the stabbed police officer.

The attack came just days after the Met staged its biggest ever terrorism exercise on the River Thames, as part of preparations for any attacks on the Houses of Parliament.