Hundreds of passengers and staff were evacuated from London City airport on Friday following a "chemical incident" that left 26 travellers feeling unwell and shut down flights in and out of the hub.
"We are treating 26 patients at the scene for difficulty breathing," the London Ambulance Service said, adding of those two had been taken to hospital.
A "hazardous area response team" had also been sent to the airport in east London, which caters mainly for business travellers and short-haul flights.
The Fire Brigade said three fire engines had been sent to the scene following "reports of a chemical incident" but did not say what the cause might be.
"Around 500 members of the public and staff have been evacuated and there are reports of a number of passengers feeling unwell," the Fire Brigade said in a statement.
London City Airport's official Twitter account said it had been evacuated "due to fire alarm".
Several incoming flights from destinations such as Frankfurt, Amsterdam and Paris had been diverted to other airports.
London City Airport is primarily aimed at business travellers and is the 13th busiest airport in Britain, with a total of 4.3 million passengers last year.