The opening of London Heathrow Airport's 4.3 billion pound Terminal 5 ended in chaos on Thursday with its new baggage handling system suspended and dozens of flights cancelled.

The state-of-the-art baggage system is meant to help smooth the journeys of millions of passengers travelling through the world's busiest international air gateway.

But the first day saw at least 33 short-haul flights cancelled and enraged passengers suffering hours of delays because of a backlog caused by technical problems.

Passengers wanting to fly late on Thursday were told they would only be able to take hand luggage onboard.

British Airways, which has its new home at T5, blamed the disruption on "teething problems".

It apologised, saying customers who had not checked-in could travel with hand baggage only, re-book or receive a refund.

Baggage handling was only one of a series of problems facing passengers. Others included car parking troubles, staff security screening and general confusion over the unfamiliar layout.

"This is not unexpected following one of the most complex and largest airport moves in history," BA said in a statement.

About 97 percent of its flights went ahead as normal, it said.

Reuters journalist Mark Jones was left sitting on a plane for two hours.

"At one point the luggage was returned to the terminal because the system said our flight had already departed," he said.

Tight security was in place in expectation of demonstrations by green protesters against the expansion of the airport.

In the event, about 200 eco-demonstrators appeared in the main entrance wearing Stop Airport Expansion T-shirts.

Authorities had been on heightened alert after a series of security breaches at Heathrow.

On the eve of the Queen formally opening the terminal this month, a man ran onto a runway, while in February, protesters broke into the airport and wrapped a banner around a plane.

The terminal is the equivalent size of about 50 soccer pitches.

The first passengers to arrive at the new terminal were from Hong Kong at 4:50 a.m., while the first outbound plane left the airport at 6:20 a.m. bound for Paris.