Update (1004ET): Despite receiving medical treatment on scene, Amess was unable to be revived and has died of his wounds, according to the Mirror.
According to Sky News, a man walked into the church around 12pm and stabbed Amess multiple times, after which the suspect was arrested on suspicion of murder, according a spokesperson for the Essex Police.
"We were called to Eastwood Road North shortly after 12.05pm. Sadly, a man later died," they said, adding "A man was arrested at the scene. We are not looking for anyone else."
One witness to the scene, Anthony Gavin Fitch, said "As I was walking across the road I saw a few people sitting on the wall outside the church and one was on the phone to the police."
"I heard it was a stabbing from a lady who was inside the church at the time. She was upset and said David Amess had been stabbed three times. She said there was an altercation and then the suspect stabbed him. I think he's still in the church, he (Sir David) hasn't been taken out."
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Conservative MP Sir David Amess was stabbed several times while attending a constituency surgery meeting at a church in Essex, according to LBC.
Armed police and forensics officers were seen outside the Belfairs Methodist Church in Leigh-on-Sea a short while ago. Amess. 69, was receiving treatment at the scene, according to Sky News. His condition is unknown.
A man has been arrested per the police.
A man's been arrested following an incident in #LeighonSea.