Conservative MP Sir David Amess has been described as a “true gent” and “a friend to everyone” following his death.
The 69-year-old, who has been an MP since 1983, was stabbed several times during a “very distressing” incident at a constituency surgery in Essex.
A suspect has been arrested.
Carrie Johnson, the Prime Minister’s wife, tweeted: “Absolutely devastating news about Sir David Amess.
“He was hugely kind and good. An enormous animal lover and a true gent. This is so completely unjust. Thoughts are with his wife and their children.”
Deputy Prime Minister Dominic Raab tweeted: “Heartbroken that we have lost Sir David Amess MP.
“A great common sense politician and a formidable campaigner with a big heart, and tremendous generosity of spirit – including towards those he disagreed with. RIP my friend.”
The Archbishop of Canterbury, Justin Welby, tweeted: “Shocked to hear of the attack on Sir David Amess. Praying for him, his loved ones and his staff.
“Our elected representatives must be able to live and work without fear of violence or intimidation if we are to maintain our democracy.”
Secretary of State for Transport Grant Shapps described Sir David Amess as “a true parliamentarian”.
He tweeted: “Awful, tragic news about David.
“A dedicated, thoughtful man and a true Parliamentarian, who lost his life while serving the constituents who he worked relentlessly for throughout his career.
“My thoughts are with his family and friends at this time.”
Health Secretary Sajid Javid tweeted: “Devastated to learn of Sir David Amess’ murder. A great man, a great friend, and a great MP killed while fulfilling his democratic role.
“My heart goes out to Julia, his family, and all who loved him. Let us remember him and what he did with his life.”
Scottish First Minister Nicola Sturgeon tweeted: “Elected representatives from across the political spectrum will be united in sadness and shock today.
“In a democracy, politicians must be accessible and open to scrutiny, but no-one deserves to have their life taken while working for and representing their constituents.”
Conservative MP for Chatham and Aylesford Tracey Crouch tweeted: “Heartbroken. I could write reams on how Sir David was one of the kindest, most compassionate, well liked colleagues in Parliament. But I can’t. I feel sick. I am lost.
“Rest in Peace. A little light went out in Parliament today. We will miss you.”
Secretary of State for Northern Ireland Brandon Lewis described Sir David Amess as “one of life’s truly nice people”.
He tweeted: “I knew David both from my days as a councillor in Essex and as a fellow MP.
“One of life’s truly nice people, a gentleman, who was always ready to give his help to anyone who needed it.
“So shocked and saddened by this awful news. My thoughts are with his family and loved ones.”
Former Conservative MP Harvey Proctor, who was Sir David Amess’s predecessor as MP for Basildon in Essex, paid tribute to him and called for security for MPs to be reviewed.
Mr Proctor told the PA news agency: “The news that my friend David Amess has been attacked and died in his constituency is horrible.
“David took over my Basildon constituency in 1983. My thoughts and best wishes go to his wife Julia and their children and his family.
“He supported me in good times and in bad. He was a wonderful Member of Parliament for Basildon and Southend-on-Sea West.
“It’s now time to consider again the security of MPs, especially when they are present at fixed events and times such as constituency surgeries.
“Our parliamentary democracy is under threat and Parliament must respond.”
Welsh First Minister Mark Drakeford tweeted: “Deeply saddened to hear about the death of Sir David Amess. A truly despicable and horrifying act.
“My thoughts are with his friends, family, and constituency staff during this distressing time.”
Communities Secretary Michael Gove tweeted: “David Amess’s passing is heart-breakingly sad. Just terrible, terrible news.
“He was a good and gentle man, he showed charity and compassion to all, his every word and act were marked by kindness. My heart goes out to his family.”
Liberal Democrat leader Sir Ed Davey tweeted: “This is tragic and horrible news. My thoughts are with David’s wife and children, the wider family, friends and David’s community.
“A truly terrible day for British politics but most importantly of all our prayers are with all the people who loved David.”
Conservative MP and former Cabinet minister David Davis tweeted: “Our thoughts and prayers are with the family, friends and staff of Sir David Amess.
“He was a thoroughly kind and decent man who above all else cared strongly for his constituents and worked hard for them over his distinguished career. We have all lost a good friend.”
Foreign Secretary Liz Truss tweeted: “Devastated to hear the terrible news about Sir David Amess MP.
“He was a lovely, lovely man and a superb parliamentarian. My thoughts are with all his family and friends.”
Chancellor Rishi Sunak tweeted: “The worst aspect of violence is its inhumanity. It steals joy from the world and can take from us that which we love the most.
“Today it took a father, a husband, and a respected colleague. All my thoughts and prayers are with Sir David’s loved ones.”
Former Tory leader Sir Iain Duncan Smith tweeted: “Shocked to hear my long time good friend/colleague has died as a result of a desperate attack in his surgery doing what all MPs have a duty to do: looking out for their constituents often as a last hope when all else has failed.
“My prayers go out to his family RIP #SirDavidAmess.”
Labour London Mayor Sadiq Khan tweeted: “I am so deeply, deeply saddened by the tragic news that Sir David has passed away.
“He loved being an MP and was a great public servant. It is just awful. My thoughts and prayers, and those of all Londoners, are with David’s loved ones at this time of unimaginable grief.”
Conservative MP Sir Roger Gale tweeted: “David and I entered the House together in 1983 and I regard him as a dear friend and a brave & compassionate MP.
“The loss to his family, who David always put first, and to the House is appalling. But David died doing what David always did – looking after his constituents.”
Speaking before Sir David’s death was confirmed, Judith Canham, deputy chair of the local Conservative club, said Sir David was a “true constituency MP” and a “friend to everyone”.
“I just can’t believe it, how anybody could harm a kind man like David I don’t know,” she told Sky News.
“I’m terribly in shock. I burst into tears as soon as I heard because we do love him dearly.”