Tory MP Sir David Amess has died after being stabbed several times at a surgery in his Southend West constituency.
The 69-year-old was attacked today at Belfairs Methodist Church in Leigh-on-Sea.
In a statement, Essex Police said officers arrived at the scene in Eastwood Road North shortly after 12.05pm and arrested a man.
A knife was also recovered from the area.
Police said they are not looking for any other suspects, and praised members of the public for their response after the incident at Belfairs Methodist Church in Leigh-on-Sea.
Aerial footage showed multiple police officers outside the church and an air ambulance at the scene.
A large cordon extended down Eastwood Road, with members of the public gathering behind it, and multiple side streets closed off.
DUP leader Sir Jeffrey Donaldson said: “Our prayers are with those closest to David. This is shocking and horrendous.
"Sir David Amess has been a long-standing friend to me personally but also to the union. More than many in Westminster, he took a keen interest in Northern Ireland and it’s people. He always wanted to see the country moving forward.
"Such a brutal attack must be condemned and is a reminder of the dangers which still face people in public office.”
The incident comes five years after Labour MP Jo Cox was murdered as she arrived to host a surgery in her Batley and Spen constituency in June 2016.
Her widower Brendan Cox tweeted: "Attacking our elected representatives is an attack on democracy itself. There is no excuse, no justification. It is as cowardly as it gets."
Witness Anthony Finch described seeing someone being taken out of the building and put into the back of a police car.
He told LBC: "At that point obviously we knew something serious had happened.
"Within five minutes we'd been informed by someone who was actually in the building what had happened, and apparently he (Sir David Amess) had been stabbed quite a few times.
"It's very odd and it's very distressing, that's for sure."
A police spokesman said: "We were called to reports of a stabbing in Eastwood Road North shortly after 12.05pm today.
"Officers were on scene shortly after, arrested a man and recovered a knife.
"He is currently in custody.
"We are not looking for anyone else in connection with the incident and do not believe there is an ongoing threat to the wider public.
"We want to thank the public who alerted us to the incident so quickly."
Police requested potential witnesses to come forward with CCTV, dashcam footage, or doorbell footage.