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The head of Virgin and his co-pilots Per Lindstrand and Steve Fossett were said to be celebrating the achievement, which provided a much needed morale boost as changing weather systems threatened their mission.

Challenger: Flew over Mount Fuji

The Virgin Global Challenger crossed the half-way mark about 1,700 miles away from the Japanese coast, and was travelling at 145mph at 31,000ft over the Pacific Ocean.

Earlier Mike Kendrick, project director, had expressed concern that the forecast lull in the weather system over the Pacific could slow the balloon down and send it backtracking towards Hawaii.

"Wind and weather and fuel are the problems we know about. It's the political ones we don't like dealing with," he said.

The BBC's Mike Donkin: "Low pressure threatened to pull the balloon down"

With the balloon is crossing the International Date Line, the crew will have an extended Christmas Eve.

Once over the line, their projected route should take them over the west coast of USA before dawn, just in time for Christmas.

Higher and faster

The expedition officials knew that the journey over the Pacific towards America would be the most hazardous part of the whole 24,000-mile journey.

Now they have spotted the wind trough they have told the pilots to take evasive action by moving higher and picking up speed.

But even if they fly calmly past the storm, problems could be stored up for later. The higher they go, the more fuel they use up.

The balloon is being swept along by a powerful jet stream at an average speed of 145mph at a height of around 30,000 feet, airplane cruising altitude. It has travelled about 10,000 miles since taking off from Morocco on 18 December, but has not yet covered half the globe.

"The next two days will be very tense," said Mr Kendrick. "We are trying to get to America for Christmas Day which will give us a good shot of crossing America on a fast jetstream."

The flight controllers plan to sing the crew Christmas carols to keep their spirits high.

The BBC's Joe Campbell: "32 hours before they see land again"

If the team were to make America's west coast they would break American millionaire Fossett's balloon distance record which he set on a previous attempt to circumnavigate the globe earlier this year.

The Pacific Mr Fossett's venture when he was forced to ditch in shark-infested waters 400 miles off the coast of Australia.

Chinese ban

As Branson's team make further headway, China has told other balloonists planning to circle the globe to hold off their attempts.

Last week, the Virgin balloon violated Chinese airspace and was told to land by the authorities. But after intervention from the British embassy, China allowed the team to carry on flying.

Rival balloon team Breitling Orbiter III said the Chinese embassy had sent a fax on Wednesday saying that, for an indefinite period, no other balloons would be permitted to enter Chinese airspace.

"In view of the behaviour of the Virgin Global Challenger," said the statement, "the competent Chinese authorities find it necessary to re-examine your overflight and ask you to postpone the departure of the balloon."

It is bad news for the four other balloon teams hoping to circumnavigate the globe.

Breitling Orbiter, piloted by Bertrand Piccard, failed to circle the world last year. He was forced to land in Burma after being refused permission to fly into Chinese air space.

"Branson's strong arm tactics are hamstringing the departure of other competitors," said the team.

Cable and Wireless wants to launch its balloon from Spain and the Spirit of Peace craft is due to lift off from Albuquerque in the United States.

Kevin Uliassi hopes to lift off in his balloon from Chicago.