British Prime Minister Boris Johnson on Saturday visited the church where lawmaker David Amess was stabbed to death a day earlier in what police say they are treating as a terrorist attack.

Amess, 69, from Johnson's Conservative Party, was knifed repeatedly in the attack at about midday on Friday in Leigh-on-Sea, east of London, during a meeting with constituents.

Johnson, interior minister Priti Patel, and leader of the opposition Labour Party Keir Starmer were among those to lay flowers in tribute to Amess at the scene of the murder.

Johnson and Starmer stood side by side in a moment of silence before leaving. On Friday, Johnson said Britain had lost a fine public servant and a much-loved friend and colleague.

In a statement early on Saturday, police said the early investigation had revealed a potential motivation linked to Islamic extremism.

Police arrested a 25-year-old British man at the scene on suspicion of murder, adding it is believed he acted alone.

Amess in the second lawmaker in little over five years to be murdered while out meeting constituents, after Jo Cox was shot and stabbed in June 2016, a few days before Britain voted to leave the European Union.