Steve Fossett, one of the greatest adventurers of modern times and the first person to achieve a solo balloon flight around the Earth, was today still missing after failing to return from a routine flight two days ago.

Fossett, who teamed up with Sir Richard Branson to achieve several world records, was last seen at 9am local time on Monday taking off solo in a small aircraft from Yerington, in western Nevada, the most mountainous state in the US.

When he did not return by noon as scheduled, a friend reported him missing. A fleet of 13 aircraft and several helicopters equipped with infra-red cameras and heat-seeking equipment led by the state’s Civil Air Patrol have been concentrating on a 600 square mile area of remote ridges, valleys and salt flats, searching for Fossett’s blue and white aircraft with orange stripes.

The search was due to resume at 7am (3pm BST) after being scaled back during the hours of darkness.

Despite growing fears for his former ballooning companion, Sir Richard remained optimistic. He said: “Steve is a tough old boot. I suspect he is waiting by his plane right now for someone to pick him up.”

Friends expressed concern however that Mr Fossett had not used either his mobile phone or the radio aboard his single-engine Citabria Super Decathlon to call for help, although mobile phone signals might well be limited by the terrain. It was reported that he had not taken a satellite phone with him.

Sir Richard said that Fossett also had a special Breitling adventurers' watch which he could use to give out a signal showing his location, but he had not done so.

"That watch, if he is conscious, he ought to be able to just pull the aerial out and that should send out an emergency signal," Sir Richard told Sky News this morning.

"Obviously the fact that he hasn't done that is worrying." It was not clear, however, if he was wearing the expensive watch for what he would have expected to be a routine trip.

Hopes were being bolstered by the fact that the plane itself was equipped with a satellite locator device that should have emitted a signal in the event of a crash landing, but had apparently not done so. A spokesman for the rescue effort said: “As far as we know it is still a rescue mission.”

Fossett was in Nevada preparing for an attempt on the land speed record at Bonneville Flats. His friend and fellow adventurer Andy Elson, a hot air balloon designer from Somerset, told Sky News this morning that Fossett may have flipped his plane and broken his radio when he tried to land on salt flats to check if they were a suitable spot for a record attempt.

"He is an amazingly rugged guy, completely at home in the outdoors," said Mr Elson. "He will be hugely embarrassed that everyone is having to look for him.

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