Terminal 3 at Heathrow Airport was evacuated today following a fire alarm.
The Heathrow Airport Twitter account said: "T3 has been evacuated following a fire alarm. We are investigating this as a matter of urgency and will provide an update shortly."
However the airport said in a subsequent tweet: "Our teams have investigated and there is no fire in T3 despite the alarm. Passengers will be directed back into the terminal shortly."
It is not yet clear what caused the activation of the alarm at around 12:30pm GMT.
The Telegraph claims those who were about to board planes were left to wait on the tarmac as the alarm brought huge disruption.
A number of flights appear to have been suspended, however those from other terminals continued to operate.
Twitter users reported lots of confusion at the airport and many passengers complained about receiving inadequate and insufficient information.