'Heathrow experienced a fire alarm activation that impacted the operation of the airfield for a short while, ' they said.
The British Airways logo is seen behind barbed wire at Heathrow Airport, west of London May 24, 2010.
British Airways cancelled and delayed flights at London's Heathrow, on Wednesday due to problems with a supplier's IT systems, the airline said.
"We have apologised to our customers for the delay to their travel plans".
One passenger was told that delays could be up to "three to five hours".
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'Emergency services responded using our regular safety procedures, and our operations have resumed'.
The control tower was evacuated and an airport spokesperson said: 'We are investigating what it means for flights landing and departing'.
Terminal 5 was further affected by the situation - leading to an organisational nightmare for BA managers.
"As a result of the temporary closure of Heathrow Airport's air traffic control tower earlier this afternoon, a small number of flights from all airlines were forced to divert to alternative airports", he added.
A BA spokesperson that "flights are operating today" and they are "doing all we can to keep disruption to our services to a minimum".
Wednesday's outage comes a year after British Airways suffered a major IT systems failure in May last year.