Heathrow Airport's Terminal 2 was evacuated after a "potentially suspicious item" sparked a security alert.
A number of police vehicles were seen outside Terminal 2 with crowds of passengers outside.
Travellers reported sniffer dogs have also arrived at the scene.
One Twitter user said: "Some kind of security alert at Heathrow Terminal 2- not sure at this point what’s happening but passengers moved outside."
Another wrote: "Search operations underway @HeathrowAirport terminal 2 due to security alert all passengers and staff evacuated sniffer dogs in duty as well."
While third wrote: "Some kind of security alert at Heathrow Terminal 2- not sure at this point what’s happening but passengers moved outside."
Heathrow Airport said in a statement: "Earlier today, our teams responded alongside Police to reports of a potentially suspicious item at Terminal 2.
"The item has been investigated and does not pose a safety risk. We thank those passengers whose journeys were temporarily disrupted for their patience, and can confirm that our operations are now back to normal."
Crowds of masked passengers were left standing outside in the rain with trolleys of luggage as the terminal was shut down.
The Metropolitan Police confirmed they had been called to reports of a suspicious item.
In a statement they said: "Police were called to Terminal 2, Heathrow, at 12.11hrs on Friday, 2 October to reports of a suspicious item.
"The item is currently being investigated. The area is currently being evacuated as a precaution."
