Police were carrying out what is believed to be a raid on a cannabis factory in Worcester Park this afternoon.
A neighbour said police swooped on the address, in Inverness Road, at 12.30pm and officers were still on the scene at 5pm.
Although police officers at the proprty refused to comment on what they were doing, evidence bags were piled up on the front lawn of the house which is in a quiet suburban street.
A neighbour said she thought the house was being rented by students.
"I've lived here for 15 years and the house has always been rented," she said.
"The last time I saw people coming and going in the house was about two or three weeks ago."
Another neighbour, who answered the door with her two small children, said the police had not given the residents any indication what was happening.
She said: "I want to know what's going on - we live in this street too.
"The police aren't saying anything but I don't want to go to bed tonight not knowing what has happened in that house - it could be a murder or anything."
Sutton police station was unavailable for comment.