Alwold Crescent, in Lee, was placed on lockdown after emergency services sped to the residential street amid concerns of a chemical reaction.
Five fire engines, paramedics and police are all on hand to deal with the incident.
The spokesperson added: "There was a smell of an unknown chemical at an address in the area and we are investigating that".
Local taxi driver Ian Crouch, 39, who was on the scene told The Sun newspaper that emergency services appeared to be focused on a sewage system.
'When I spoke to a policeman he said there were people complaining of irritation, who had been throwing up all morning.
"They've been rushed into hospital".
Residents were told by police they were investigating whether the incident was terror-related.
Homes were evacuated and several people taken to hospital after a "chemical incident" in south-east London.