The British Metropolitan Police has classified the killing of Conservative MP David Ames as a "terrorist act" after he was stabbed during a visit to his constituency in Essex, southeast England.

In a statement, Dean Haydon, deputy commissioner of the London Police Service and National Counter Terrorism Coordinator, said the incident was "terrorism-related".

Haydon said an initial investigation showed that the attack may have been caused by religious extremism.

In a statement, the London police announced that the investigation was conducted by the Anti-Terrorism Unit, noting that the attacker was a 25-year-old citizen - whose name was not revealed.

Sky News said that the arrested man has British citizenship and is of Somali origin, and the Daily Telegraph reported that the detainee is believed to be Somali.

The Conservative MP, led by Prime Minister Boris Johnson, was killed after being stabbed several times on Friday by a man who entered a meeting between the MP and members of his constituency at Belvers Baptist Church.

Police forces entered the church and said they had arrested a man and were not looking for anyone else in connection with the incident.

Police added that Representative Ames was treated by emergency services but died at the scene.

Ames was first elected to Parliament to represent Basildon in 1983, and then ran for election in Southend West in 1997.

House of Commons Speaker Lindsey Hoyle said the security of MPs would have to be discussed.

The MP's colleagues from various parties expressed their shock and praised him as one of the oldest current legislators, and that he regularly met with his constituents on the first and third Fridays of every month, saying that he was loyal to the constituency he represented.

Flags were flown at half-mast in Downing Street to mourn the slain MP.

This incident recalls what happened in 2010 when Labor MP Stephen Thames survived a similar attack in his constituency office, as well as the killing of Labor MP Jo Cox in the 2016 shooting just days before the Brexit referendum.