Killing of British MP 'an act of terror'

The widower of murdered British MP Jo Cox says her killing was an act of terror as he paid tribute to his late wife alongside hundreds of mourners at an emotional memorial in London's Trafalgar Square.

Cox died after she was shot and stabbed in the street in her constituency in northern England last week - an attack that shocked the country and prompted an outpouring of sympathy around the globe for the lifelong humanitarian campaigner.

"Jo's killing was political. It was an act of terror designed to advance an agenda of hatred towards others," Brendan Cox said in a tearful speech.

"What a beautiful irony it is that an act designed to advance hatred has instead generated such an outpouring of love."

The Wednesday vigil marking what would have been her 42nd birthday, and also attended by Nobel laureate Malala Yousafzai, fell silent at 1518 GMT (0018 AEST) in a mark of respect also observed at other events across the country and around the world including in Beirut, Brussels, Melbourne, Nairobi, Geneva, New York and Washington.

Cox's death has abruptly changed the tone of the final days of caustic campaign around a referendum on Britain's European Union membership, which takes place on Thursday, prompting a groundswell of support for a more positive campaign.

Cox's husband and their young son and daughter, whose London home was a houseboat, earlier waved to clapping crowds as they arrived by boat after mooring a dinghy filled with flowers in the River Thames outside the Houses of Parliament.

Before her election to parliament in May 2015, Cox had spent almost a decade working for aid agency Oxfam.

A fund set up in her memory has so far raised STG1.3 million ($A2.55 million).

Malala, who in 2014 became the youngest ever winner of the Nobel Peace Prize for her work promoting women's access to education, said: "Jo's life is a proof that a message of peace is more powerful than any weapon of war. Once again the extremists have failed."