Tributes have been paid around the world to Labour MP Jo Cox, who died after being shot and stabbed.
The 41-year-old was attacked before holding a constituency surgery in Birstall, West Yorkshire on Thursday.
Among those who honoured Mrs Cox was Hillary Clinton, the US Democratic Party's presidential hopeful, who said: "It is cruel and terrible that her life was cut short."
Mrs Cox's husband said the mother of two had fought for "a better world".
Her attacker is reported to have shouted "put Britain first" at least twice. A 52-year-old man, named locally as Tommy Mair, has been arrested.
Vote Leave and Remain have both suspended campaigning in the EU referendum in light of the attack.
Witness Ben Abdullah, who was working at a café next to the scene of the attack, said he saw "a river of people" coming down the street "screaming and shouting".
"I wasn't frightened... I don't know what I was. I thought, 'it's like a warzone'", he said.
Mr Abdullah said he heard several shots and saw Mrs Cox on the floor "in a very bad state".
Prime Minister David Cameron and Labour leader Jeremy Corby plan to visit Mrs Cox's constituency together later.
Mrs Clinton said it was "critical" Britain and the United States "stand together against hatred and violence".
Another US politician, Gabrielle Giffords, who was the victim of an assassination attempt in 2011, wrote on Twitter that she was "absolutely sickened" by the killing, praising Mrs Cox as "young, courageous, and hardworking. A rising star, mother, and wife".
Tributes have been paid from across Europe to Mrs Cox, who had campaigned for Britain to remain in the EU.
Rachel Reeves, Labour MP for Leeds West, said: "Jo was so loved in her community she was part of it and MPs, if they are going to do their job, need to be part of their community to do these advice surgeries.
"We can't let the behaviour of one man destroy that link between MPs and their constituencies."
Politicians have been warned to review their security in the wake of the attack and a reminder of safety guidance has been sent out to MPs, said a government spokesman.
Most MPs are continuing with constituency surgeries.
On Thursday, hundreds of people of all faiths packed into Saint Peter's Church in Birstall for a service of remembrance while a vigil was also held outside Parliament.
Churches in the parish of Batley have announced they are to remain open on Friday for those wishing to pay their respects.
The Rt Rev Dr Jonathan Gibbs, The Bishop of Huddersfield, said: "All of us held Jo in enormous affection and respect. The sadness is seeping into us more deeply."
"I was privileged to know Jo, it's going to be a really tough day we'll be drawing deep on the resources of our faith."
Labour leader Jeremy Corbyn was among several British politicians to attend an impromptu vigil in Parliament Square in central London on Thursday evening.
Mr Corbyn had earlier paid tribute to Mrs Cox, saying the country would be "in shock" and describing the MP as a "much-loved colleague".
Prime Minister David Cameron said: "The death of Jo Cox is a tragedy. She was a committed and caring MP."
At the scene, Clare McDonnell, BBC 5Live
I'm standing in the market square at the top of Market Street about 100 yards from the blue and white police tape lines where Jo was stabbed and shot.
The aroma of flowers is quite overpowering, people here have been leaving tributes here last night and this morning.
There's a note that says, "RIP Jo Cox, a friend and a fantastic campaigner. A bright, shining star has gone out tonight".
Tributes have also come in from around the world, reflecting the international profile she had before she became an MP in Westminster.
Conservative MP Andrew Mitchell, who together with Mrs Cox set up the All Party Parliamentary Working Group on Syria, described her as a "force of nature".
Writing in the Daily Telegraph, he said she had been a "five foot bundle of Yorkshire grit and determination absolutely committed to helping other people".
Mrs Cox is the first sitting MP to be killed since 1990, when Ian Gow was the last in a string of politicians to die at the hands of Northern Irish terror groups.
West Yorkshire Police have so far refused to discuss the possible motive behind the killing despite reports that Mr Mair had sympathy for far-right groups.
Political party Britain First, which boasts of its hatred of white left-wing politicians, issued a video statement condemning the attack and said that it had no connection with the incident.
Mrs Cox was married to campaigner Brendan Cox, and she had two young children, with the family dividing its time between its constituency home and a river boat on the Thames.
He said in a statement: "Jo would have no regrets about her life, she lived every day of it to the full.
"Jo believed in a better world and she fought for it every day of her life with an energy and a zest for life that would exhaust most people."
A Buckingham Palace spokesman has said the Queen would write privately to Mrs Cox's husband.