His ground crew said his emergency locator beacon had been triggered shortly after he headed into thunderstorms.

Fossett: Emergency signal from the Pacific

They said a signal has been picked up by satellite allowing rescuers from Australia to pinpoint the balloon's location for their search.

There was no word on whether the millionaire balloonist was OK.

Alan Blount, director of the balloon's mission control says: "A lot depends on how fast he came down."

His balloon is designed to float, and is carrying a life raft.

This is Fossett's fourth attempt

Australia has sent a military plane to look for him.

Fossett was making his fourth attempt to become the first person to fly non-stop in a balloon around. He had covered two-thirds of the journey.

The balloon was 500 miles (800km) off the Australian coast heading toward its final destination of Argentina, South America, when contact was lost.

The 54-year-old millionaire has already broken a number of records on his trip, which started in western Argentina.

He became the first man to fly a balloon over the Indian Ocean; he has established what is believed to be a new long-distance record of nearly 18,000km and has completed the longest continuous manned balloon flight over water.