London City Airport has been evacuated after reports of a "chemical incident", London Fire Brigade said.
There were reports that a number of passengers felt unwell, the brigade said.
The alarm was raised at 4.11pm on Friday.
Around 500 members of the public and staff were evacuated.
A spokesman for LFB said: "Three fire engines and a range of specialist appliances have been called to reports of a chemical incident at London City Airport this afternoon.
"Around 500 members of the public and staff have been evacuated and there are reports of a number of passengers feeling unwell.
London Ambulance Service said they were at the scene, but have yet to confirm if there are any injuries.
LFB said the cause of the incident was not yet known.
All flights were suspended and several incoming planes from destinations such as Frankfurt, Amsterdam, Belfast City and Paris were diverted to other airports.