Police have been called to a report of a suspicious package at London City Airport, hours after security alerts at Heathrow and Waterloo station.
Scotland Yard said Aviation House, which contains London City's head offices, had been evacuated "as a precaution".
Earlier, Heathrow's headquarters were also evacuated following what an airport spokeswoman described as a "criminal act".
Specialist officers were sent to assess all three packages but police said it was too early to confirm if they were linked.
The Metropolitan Police was called to London City at 12.10pm and closed the airport's DLR station and surrounding roads.
Thirty minutes earlier, British Transport Police was alerted to a suspicious package at London Waterloo rail station. The station has not been evacuated.
Police were also called to the Compass Centre, which houses Heathrow's administrative headquarters, just before 10am. The building was evacuated but flights were not affected.
A Heathrow spokeswoman said: "Police response teams and the emergency services attended quickly, enabling colleagues to evacuate safely without injury.
"The police are treating this as a criminal act and we will be assisting with this investigation.”
Flights were not disrupted at either airport.
DLR services have since resumed at London City.
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