British Prime Minister Boris Johnson has paid tribute to his Conservative colleague David Amess, who was stabbed to death in his constituency office in southeast England, lauding him as "one of the kindest, nicest, most gentle people in politics".

Mr Amess, 69, was attacked this afternoon at Belfairs Methodist Church in Leigh-on-Sea, Essex.

A 25-year-old man was arrested at the scene on suspicion of murder.

"I think all our hearts are full of shock and sadness today at the loss of Sir David Amess MP, who was killed in his constituency surgery, in a church, after almost 40 years of continuous service to the people of Essex and the whole of the United Kingdom," Mr Johnson told reporters.

Speaking this evening, he said: "David was a man who believed passionately in this country and in its future.

"And we've lost today a fine public servant and a much-loved friend and colleague, and our thoughts are very much today with his wife, his children, and his family."

David Amess

Mr Amess is the second sitting MP to be killed in such circumstances in five years, following the death of Labour MP Jo Cox in 2016 as she attended a constituency surgery.

When asked about whether Mr Amess' death highlights a problem with the security protection of MPs, Mr Johnson said: "I think what we need to do now is let the police get on with the investigation.

"I am sure that all those issues will be considered in the proper time but I think this is a moment for us to think of Sir David, his wife, his family and our thoughts are very much with them."

Northern Ireland's political leaders have also paid tribute to Mr Amess.

First Minister Paul Givan and deputy First Minister Michelle O'Neill have expressed their shock and sympathy.

"This was a brutal attack on a man with a distinguished history of public service, and the repercussions will resonate with us all," Mr Givan said.

"But, more than this, Sir David was a husband, father and colleague - and it is those closest to him who will feel this loss most profoundly. My immediate thoughts are with Sir David's family and friends at this very sad time."

Ms O'Neill said: "I was deeply shocked to learn of the death of David Amess in the most tragic of circumstances. No public representative should face attack when carrying out their duties on behalf of their constituents.

"My thoughts and prayers, first and foremost, are with David's family and friends at this awful time."

Secretary of State for Northern Ireland Brandon Lewis described Mr 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."

Flags above No 10 Downing Street lowered to half mast in tribute to David Amess

Labour Party leader Keir Starmer tweeted: "Horrific and deeply shocking news. Thinking of David, his family and his staff."

Former British prime minister David Cameron said it was "the most devastating, horrific and tragic news".

"David Amess was a kind and thoroughly decent man. Words cannot adequately express the horror of what has happened today. Right now, my heart goes out to David's family."

Former British prime minister Theresa May has also paid tribute to Mr Amess, describing him as a "decent man and respected Parliamentarian, killed in his own community while carrying out his public duties.

"A tragic day for our democracy. My thoughts and prayers are with David's family."

David Amess with Former Prime Minister Theresa May

Communities Secretary Michael Gove said that Mr Amess's death is "heart-breakingly sad".

"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."

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."

Taoiseach Micheál Martin said on Twitter that he was "truly shocked to hear of the death of British MP David Amess, killed while holding a clinic in his constituency office. My deepest sympathies to his wife Julia, children, family and friends".

Tánaiste Leo Varadkar said that he was shocked and saddened to hear about Mr Amess' death.

In a post on Twitter, he said: "Shocked and saddened to hear about this. My sincere condolences to David Amess's family, friends, constituents and colleagues.

"Nobody anywhere, including in politics or public service, should have to fear for their safety while doing their work."

Minister for Foreign Affairs Simon Coveney tweeted: "What a shocking and tragic incident. Our thoughts and sincere sympathies are with family, friends and political colleagues of Sir David Amess MP."

Also on Twitter, Sinn Féin leader Mary Lou McDonald said she was "horrified to hear news of the fatal stabbing of David Amess MP. Thoughts and prayers with his family, friends and colleagues".