LONDON — UK police declared the fatal stabbing of Sir David Amess a terrorist incident as the investigation into the incident continued.

The Conservative member of the UK Parliament, from Southend West, was stabbed at a constituent meeting at a church and died at the scene.

"The early investigation has revealed a potential motivation linked to Islamist extremism," UK police said in a statement overnight.

Police arrested a 25-year-old man on suspicion of murder after the attack, which happened around midday on Friday in the English coastal town of Leigh-on-Sea.

UK police say it is believed the man acted alone but enquiries into the incident are being carried out with police carrying out searches at two addresses in the London area.

Boris Johnson said he was "full of shock and sadness" at the death of the 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."

Johnson, who laid flowers at the scene on Saturday, said he was one of the "one of the kindest, nicest, most gentle people in politics".

British politicians paid tribute to the MP and expressed their shock over the incident.

Labour's Sir Keir Starmer, who went to Essex with the PM, hailed Sir David's "profound sense of public duty".

Commons Speaker Sir Lindsay Hoyle said he was a "bright light of Parliament".

The Duke and Duchess of Cambridge said they were "shocked and saddened" by the death of Sir David, who "dedicated 40 years of his life to serving his community".

A Conservative backbencher for nearly 40 years, Sir David entered Parliament as the MP for Basildon following the 1983 general election.

He switched seats in 1997, when he was elected MP for nearby Southend West — the Essex constituency he represented until his death.

His constituents have spoken of their shock at his killing, with residents choking back tears as they spilled on to the streets after his death.

Conservative councilor Kevin Buck said the MP had "died doing what he loved — meeting the people and helping the people".

Speaking to BBC Essex, Judith Canham, the former deputy chair of the Southend West Conservative Association, said Sir David had a "photographic memory".

"Sometimes I'd be out canvassing with him and he'd see someone he hadn't seen for a long time and he'd say 'how was your hip operation?'"

Virginia Lewis-Jones, the daughter of Dame Vera Lynn, says Sir David was a passionate supporter of a proposed memorial to the late singer.

She said he would "grab it like a terrier" when he committed himself to campaigning on any issue.

Fellow Tory MP Andrew Rosindell said Sir David was his "oldest friend" in Parliament, and he felt "sick inside at what has happened". "We've all lost a very special person in our lives," he added.

Labour MP Harriet Harman entered the House of Commons in 1982, one year before Sir David and remembers it as a "polarized" time.

Speaking to the BBC's Today program, she said had been "determined not to have friendly relations with any Conservative MPs, but it was impossible to sustain that with David Amess because he was so friendly and so determined to work with MPs on other causes".

For premier Theresa May said his death was "heartbreaking" and a "tragic day for our democracy". She added that Sir David was a "decent man and respected parliamentarian, killed in his own community while carrying out his public duties".

Former prime minister David Cameron called Sir David a "thoroughly decent man" and "the most committed MP you could ever hope to meet".

Sir David is the second MP to be killed in the past five years, following the murder of Labour MP Jo Cox in 2016.

She was killed outside a library in Birstall, West Yorkshire, where she was due to hold a constituency surgery.

Jo Cox's sister Kim Leadbeater, who is now the Labour MP for the Batley seat she represented, said she was "totally shocked to think that something so horrific could happen again to another MP and family". — Agencies