Britain's Parliament was placed on lockdown on Wednesday after a man drove a large vehicle into at least five people on Westminster Bridge and then stabbed a police officer.

The knife assailant was then shot several times by police officers as he tried to access the Palace of Westminster, in what officials are calling a "terrorist incident."

Security described the suspect as a middle-aged Asian man holding a seven-to-eight inch knife, who rammed into the railings of the Palace of Westminster right after mowing down citizens on the bridge.

At least one woman was killed by the motorist, while many others are reported to be experiencing "catastrophic" injuries, according to The Telegraph.

Prime Minister Theresa May was rushed into a vehicle and driven back to her office, where she was eventually reported to be safe.

Parliament has been suspended and the story is still developing.

Update: Police have confirmed that four people have died in the attack so far, including the stabbed police officer and the attacker. At least 20 people have been injured, including three French high school students who were visiting London on a school trip.