A hardy group of 181 passengers boarded a jet at Singapore airport yesterday for the world's longest commercial flight - an inaugural non-stop service to New York designed to appeal to time-pressed Asian and American business executives.

After a champagne send-off accompanied by a band blasting out "New York, New York", the Singapore Airlines plane embarked on an 18-hour, 8,900 nautical mile journey over the North Pole which has drawn criticism from experts on medical and commercial grounds.

Airline staff handed out 20,000 red apples to mark the record, which uses a new ultra long-range Airbus A340-500 plane with enlarged wings, enhanced engines and a smaller, lighter body than traditional passenger aircraft.

Singapore Airlines said it would knock four hours off a one-stop service and would cut down on delays. A spokesman, John Cotton, said: "If you've got an intermediate stop-off point you're at the mercy of air traffic control and various other factors, which can be very inconvenient."

The new Airbus plane has a long enough range to fly non-stop between London and western Australia. But doctors have expressed concern about the impact on the body of such long unbroken flights, in which passengers will constantly breathe recycled air.

Experts said passengers had a greater chance of picking up viral infections such as flu and colds on board. Farrol Kahn, director of the Aviation Health Institute, said the heart and lungs would come under increased strain from a lower than usual supply of oxygen, with an enhanced risk of deep vein thrombosis (DVT) among people who fail to exercise frequently on board.

"We'd like to see doctors on board these very long flights," said Mr Kahn. "There is an increased risk of medical incidents across the board - whether it's heart attacks, DVT, fainting or alcohol abuse."

Singapore Airlines has equipped its new aircraft with special cupboards big enough to take a corpse in case any passengers die en route.

The planes are staffed by 14 cabin crew and six flightdeck officers, each working four-hour shifts. A special "passengers' corner" on board allows people to chat or "network" during the flight.

The flight requires 222,000 litres of fuel, weighing more than 10 times as much as the passengers. Jeff Gazzard, of the environmental organisation AirportWatch, said the service would mean less noise pollution than a stopping service. However, he said there was little advantage in fuel consumption because of the need to use more energy at the beginning of the flight to power its heavy load. "I would expect there to be a marginal environmental advantage in stopping en route," he said.

Return tickets on the route cost £700 in premium economy class or £2,900 in "Raffles" business class.

But industry watchers queried the long-term commercial case for the service. Kieran Daly, group editor of Flight International, said Airbus had struggled to attract orders for the long-range plane, which is only suitable for a small number of routes.

Mr Daly said that even among business passengers there was often a preference to stop for a break during long journeys: "An 18-hour flight is a pretty tough experience. It's not yet clear that passengers are really going to leap at the chance of flying these kind of distances non-stop."