LONDON (AP/CBS) – A car rampage and knife attack in London left four people dead, including a police officer guarding Parliament and an attacker, police said. At least 20 people were wounded.

A vehicle mowed down pedestrians on London’s Westminster Bridge Wednesday around the same time a knife-wielding attacker stabbed a police officer and was shot on the grounds outside Britain’s Parliament, sending the compound into lockdown. That attacker was killed by police.

An aerial view of the scene outside Parliament in London on Wednesday afternoon. (CBS)

London’s Metropolitan Police said they were treating the incident as suspected terrorism.

A session of Britain’s House of Commons was suspended as witnesses reported hearing sounds like gunfire nearby. The Commons’ speaker suspended the session as police responded to an incident, CBS New reports.

A doctor said some of the wounded had “catastrophic” injuries, after a vehicle apparently hit pedestrians on Westminster Bridge, near Parliament.

“There were people across the bridge,” said Colleen Anderson of St Thomas’ Hospital. “There were some with minor injuries, some catastrophic. Some had injuries they could walk away from or who have life-changing injuries.”

Westminster Bridge is just outside Parliament. Witnesses said in addition to the gunfire, the vehicle on the bridge then crashed into a gate. A medivac helicopter landed in the area as police cordoned off the streets in the area.

An Air Ambulance at the scene by Westminster Bridge and the Houses of Parliament on March 22, 2017 in London, England. (Credit: Jack Taylor/Getty Images)

The leader of Britain’s House of Commons, David Liddington said one police officer was stabbed inside the gates of the compound and the “alleged assailant was shot by armed police.” Liddington also said there were “reports of further violent incidents in the vicinity.”

A member of the public is treated by emergency services near Westminster Bridge and the Houses of Parliament on March 22, 2017 in London, England. (Credit: Carl Court/Getty Images)

The motive at this point in unclear. It appears that an active manhunt is still underway. British Police said they are treating this attack as terrorism.

Prime Minister Theresa May was inside Parliament at the time of the attack. CBS was told she has been evacuated and is safe.

The White House says U.S. President Donald Trump has been briefed on a gun and knife incident at Britain’s Parliament in London. Trump himself said during a brief appearance Wednesday before reporters at the White House that he was just getting the news. He called it “big news.”

Trump’s spokesman, Sean Spicer, said that the U.S. will continue to monitor the situation and update the president.

The U.S. State Department said it is closely monitoring the incident outside London’s Parliament and urged Americans in London to avoid the area.

Spokesman Mark Toner said Wednesday: “We stand ready to assist in any way the U.K. authorities would find helpful.”

He added that the U.S. Embassy in London is closely following the news and stands ready to help any affected Americans.

He said: “Our hearts go out to those affected.”

The area in which the incidents took place are popular tourist sites. The area has been blocked off and metro stations in the area were shutdown as an investigation was underway.

The incident comes exactly one year after a double suicide bombing attack on Zaventem Airport in Brussels, Belgian. Thirty-two people lost their lives and over 300 people were injured. ISIS was behind that attack.

Locally, Illinois State Police said they are monitoring intelligence reports regarding the attack, saying their thoughts and prayers are with the London victims and their families.

The story is developing. Check back for updates.

(CBS Chicago and The Associated Press contributed to this copy. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.)