British Airways cancelled more than a 100 flights over the weekend following a chaotic opening of its new $8.6 billion terminal at London's Heathrow airport.

It said it had cut 66 short-haul and European flights yesterday and would cancel 37 more today after Terminal 5's grand opening last Thursday descended into chaos when its new baggage handling system ground to a halt.

The launch of the terminal building designed by architect Richard Rogers has proved a public relations disaster for the carrier that once styled itself the 'world's favourite airline'.

It has forced the postponement of an advertising campaign promoting the new terminal which was due to have been launched next week, a BA spokeswoman said.

BA Chief Executive Willie Walsh has apologised for the disruption and admitted the move to the terminal was "definitely not our finest hour".

BA shares fell more than three per cent on Friday, hit by the Heathrow chaos and jitters ahead of today's start of an 'open skies' deal to create greater competition on trans-Atlantic routes.

The airline faces a sizeable compensation bill for passengers delayed and forced to stay overnight in hotels.

It cancelled 68 flights on Thursday and 72 on Friday. Terminal 5 is Britain's largest enclosed space, equivalent to the size of about 50 soccer pitches. It was touted as the answer to regular delays at the airport. British Airways spent months promoting the gleaming terminal, packed with high-end shops and restaurants, bringing photographers and journalists from all over the world to show off the complex.