London City Airport declared safe after 'chemical incident' left dozens needing treatment
Hundreds of passengers ordered to leave terminal as all flights stopped
Police investigating the suspected chemical incident which led to the evacuation of London City Airport have discovered what is "believed to be a CS gas spray", a spokesman said.
The find came after police and firefighters scoured the airport following the alert, which saw dozens of passengers treated for breathing difficulties.
The airport spokesman said it was unclear what had caused the chemical incident, but officers were "investigating whether it was the result of an accidental discharge of the spray".
Two casualties were taken to hospital and 25 were treated at the scene, London Ambulance Service (LAS) said.
A spokesman for London Fire Brigade (LFB) said it was called to the airport at 4.11pm to "reports of a chemical incident".
A "full evacuation of the airport terminal" saw around 500 members of the public and airport staff forced to leave.
The airport, which reopened after being declared safe at around 7pm, was said to have closed after an alarm was activated.
Passengers described the situation as "quite scary", with airport staff jumping over check-in desks to escape.
Passengers were warned that further disruption to flights was expected.
An LFB spokesman said "two complete sweeps of the airport building" were carried out jointly by firefighters and police officers wearing protective equipment.
He added: "No elevated readings were found and the building was ventilated, searched and declared safe."
Medics trained to treat people in hazardous situations also attended the scene.
LAS assistant director of operations Paul Gibson said: "All patients were treated for minor breathing difficulties and two were taken to hospital."
David Morris, who was one of the passengers caught up in the incident, said he was at the check-in desk for his BA flight to Edinburgh when people started coughing.
"We were queuing up and we were just about to check our bags in, and I was talking and started to cough to the point I was not able to keep talking," the 28-year-old told the Press Association.
"It was getting quite bad and we saw other people starting to cough at the same time. The people behind the desk were coughing the most and quite aggressively.
"Within two minutes, they shouted for everyone to get out."
Mr Morris said BA staff behind the check-in desk jumped over to escape, calling the situation "quite scary".
He said that whatever was causing people to cough did not smell or have any colour to it.
''Everyone was shouting and rushing towards the door,'' he added.
Once outside, he said those who had been coughing, between 15 and 20 people, were sectioned off and checked over by paramedics.
The closure of the airport led to travel chaos as all flights were suspended.
Several incoming planes from destinations such as Frankfurt, Amsterdam, Belfast City and Paris were diverted to other airports.
A group of Scottish MPs were among the travellers left standing on the airport's tarmac for more than 90 minutes before being allowed back into the terminal building.
SNP MP Calum Kerr, who was unhappy after a proposed bill for an automatic pardon for gay men convicted of now-abolished sexual offences was not put to a vote in the House of Commons, said: "This is just the perfect end to a day when we've seen democracy let us down and now the transport system has let us down.
"News agencies were reporting a chemical incident, which obviously changed the atmosphere a bit. People are less fraught. It goes from being a pain in the derriere to a case of: 'Is everybody safe? I hope people are okay'."
Ross Edgar, 28, from Glasgow said he heard an alarm going off at around 4.15, resulting in everyone being evacuated from the building.
Large queues comprised of hundreds of people, hoping to get into the airport, could be seen making its way around the entrance of the terminal once it had been declared safe.
Airport staff using megaphones informed those waiting of the flights which were cancelled and those which may take off. At least 11 flights were listed as cancelled.
Inside the terminal the waiting ensued, as the checkin area continued to heave with people eager to reach their destination.
A nearby Travelodge also took the brunt of the chaos, with queues out of the door as those left stranded by the incident tried to find somewhere to stay.
A London City spokesman said: "We apologise to passengers for the inconvenience caused today when an alarm was activated, triggering a full evacuation of the airport terminal.
"Passengers were evacuated safely and we thank them for their patience.
"Following the evacuation, some individuals reported feeling unwell and were treated at the scene by London Ambulance Service.
"Emergency services responded to the evacuation, citing a possible chemical incident, with firefighters and police officers jointly conducting sweeps of the airport building.
"The search of the airport led to the discovery of what is believed to be a CS gas spray.
"Whilst the cause of the incident has yet to be confirmed, officers are investigating whether it was the result of an accidental discharge of the spray.
"The airport was declared safe and reopened at approximately 1900. Passengers are advised to contact their airline for the latest information regarding their flights."
The Met Police said it was investigating whether the CS gas had been "discarded by a passenger prior to check-in".