LONDON - Tributes are pouring in for the police officer who was fatally stabbed in the London attacks on Wednesday (March 22), with many hailing him as a true hero.

Keith Palmer, 48, was unarmed when an attacker with two large knives came charging towards him outside Parliament, after mowing down pedestrians in his car on Westminster Bridge.

Palmer was a member of the Parliamentary and Diplomatic Protection Command with 15 years of experience, said Metropolitan Police Counter-Terror Commissioner Mark Rowley.

"He was someone who left for work expecting to return home at the end of his shift and he had every right to expect that would happen," Rowley told reporters.

Greater Manchester Police Chief Constable Ian Hopkins said: "#RIP PC Keith Palmer, brutally murdered today carrying out his duty helping to protect Parliament and the freedom of our Country."

Paramedics had fought to save Palmer, with British Foreign Office Minister Tobias Ellwood among those who rushed to help, according to media reports.

Mr Ellwood, who lost his brother in the 2002 Bali bombing, could be seen pumping the officer's chest, Agence France-Presse (AFP) reported.

Palmer's former colleague, Conservative MP James Cleverly, said on Twitter that the police officer was a "lovely man".

"I've known Keith for 25 years. We served together in the Royal Artillery before he became a copper. A lovely man, a friend. I'm heartbroken," Cleverly said in his tweets.

"My thoughts are with the family, friends and colleagues of Pc Keith Palmer. A brave man."

Some Members of Parliament who were caught in the lockdown after the attack also paid their tribute to the police officer.

"Going to bed alive, safe and well thanks to Pc Keith Palmer. God bless him, his family and all those killed or injured. Terror will not win," tweeted Labour MP Barry Gardiner.

Other Londoners have also taken to social media to express their respect and defiance after the attack, using hashtags #WeAreNotAfraid and #PrayForLondon.

"#WeAreNotAfraid so will do my usual run through London, except today I know the name of one of the many bravo heros #keithpalmer - RIP !" said a Twitter user known as Gary.

"Husband, Father, Policeman, Hero. Thank you," said a woman named Debs.