It has apologised for the "global system outage" and indicated that it was "working to resolve the problem".

Heathrow Airport said it was working closely with British Airways to solve the issue.

The airline told the BBC that at this stage it has no evidence to suggest the system failure was caused by a cyber attack.

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It has since asked passengers with flights before 18:00 BST on Saturday not to come to Gatwick or Heathrow airports, which it said had become "extremely congested".

Passengers affected will be offered the option of rescheduling or a refund.

Meanwhile, other airlines flying in and out of Heathrow and Gatwick are not affected.

The situation means that parts of BA's website are unavailable and some travellers said they could not check in on the mobile app.

Travellers have been told to check ba.com and its Twitter Account for updates about the situation.