Sussex astronaut Piers Sellers has spoken of his shock at hearing seven astronauts were feared dead after Nasa lost contact with the space shuttle Columbia today.

Nasa lost contact with the craft as it re-entered the Earth's atmosphere before landing.

Columbia had been due to touch down in Florida at 1416 GMT and was at an altitude of 200,700ft and travelling at 12,500mph when communication went silent.

There were reports of small explosions and smoke being seen as the shuttle flew over the state of Texas.

47-year-old Piers Sellers, from Crowborough, East Sussex, became only the third Briton to go into space last year when he joined a mission on board the shuttle Atlantis.

Clearly distressed after watching events unfold in the skies, he told reporters from his home in Houston, Texas: "Three or four of my friends are on board.

"We don't know the details, what's happening or the causes. But it's obvious that the vehicle broke up during entry and we can't say much more than that. The vehicle is lost.

"During entry, they were coming into land at Florida. Their trajectory took them over north Texas then some people saw a single trail break into others.

"There were then minor explosions and puffs of smoke and communication was lost."

Dr Sellers completed an 11-day mission to the international space station in the Earth's orbit last October.

In doing so, the scientist followed in the footsteps of Helen Sharman and Michael Foale, two other British-born astronauts to launch into orbit.

He also spent 19 hours and 41 minutes walking in space.

The father-of-two, who obtained US citizenship to become an astronaut, said re-entry into the Earth's atmosphere exerts massive pressures on the Shuttle.

"The main pressure is from thermal stress on the vehicle and a sort of air ramping effect on the Shuttle," he explained.

"I never thought I would see this on entry. The attention for this sort of thing is usually focused on take-off. It's terrible. But it goes to show it's a dangerous business."

Dr Sellers said that an "agency-wide response" would follow, going into every detail of what happened.

The tragedy is the first accident during descent to Earth or landing in 42 years of US human space flight.

On January 28, 1986, space shuttle Challenger exploded shortly after lift-off, killing all seven astronauts on board.

Nasa commemorated the anniversary of the event last week and that of the Apollo space craft fire that killed three on January 27, 1967.