A terminal at Heathrow was evacuated on Tuesday because of a suspicious bag, police said.
A police spokeswoman said she had no further details about the incident at Terminal 2, which serves European destinations.
A man was seen running in and dropping a bag at the check-in area, airport personnel said.
A nearby administrative building at Heathrow, one of the world's busiest airports, was also evacuated.
Passengers were being kept about 300 yards (metres) away from the terminal, a witness said.
We'll update this as we get more info.