Homes were evacuated and two people taken to hospital after a "chemical incident" in south-east London.
Emergency services were called to Alwold Crescent in Lee at 09:50 BST over fears residents were suffering reactions to an unknown chemical smell.
Nine people, including the two taken to hospital, were assessed by paramedics after reports of nausea and vomiting.
London Fire Brigade (LFB) said it had swept the area but found no raised levels of chemicals or toxins.
The cause of the incident is still unknown but a brigade spokeswoman said crews had completed investigations and "are handing over to the gas board".
Scotland Yard said the incident was not believed to be crime-related.
A cordon was set up in the crescent at about 11:30 and residents in four houses were asked to leave their homes.
Wayne Higgins said he and others living in the area had been feeling unwell for a number of days but "we just assumed everyone had a cold or something was going round".
"For the moment we don't know when we will be allowed back in - not until they find out the cause of the problem," he said.
Kevin Dobbins, who was also evacuated said he had not felt the effects but "I know neighbours who were experiencing sickness".
He said investigators had told residents they had ruled out a few different things and "believe it could be a small gas leak".
Five fire engines, along with paramedics and police were all deployed to the area.
A spokeswoman for the brigade said 21 people were evacuated from houses "as a precaution".
London Ambulance Service (LAS) said it had sent two ambulance crews along with members of the hazard response team.
A spokesperson for Southern Gas Network (SGN) said engineers were carrying out routine safety checks in the immediate area "as part of the ongoing investigation".