Two workmen were killed and another seriously injured today when a crane collapsed at a school building site.

Witnesses said it toppled over and crashed into a neighbouring crane at Durrington High School, Worthing.

The wreckage fell on to the shell of the new £11 million Highdown School for children with special needs which is being built in the north west corner of the school grounds.

No children were hurt in the incident, which happened at about 10.15am.

The death toll could have been higher if many of the workmen had not been taking a break in the canteen.

The two men who died, employees of contractor Willmott Dixon, were thought to have been working on the crane and were killed instantly as it crashed to the ground.

The man who received head injuries is a workman in his 50s.

The second crane remained standing, with its huge jib snapped and dangling at right angles over the new school building at the junction of Littlehampton Road and The Boulevard.

Tim Hewell, 48, of Raglan Avenue, said: "I live behind the construction site and I was outside when there was this huge noise which made hundreds of seagulls fly into the air.

"It sounded like lots of bricks dropping. It was very loud and went on and on as if there was stuff tumbling. I immediately thought there might have been a road accident but I walked around the corner and the crane had snapped.

"It was dangling like a broken arm."

The new Highdown school is being built to replace an ageing complex of the same name just yards away on the opposite side of Littlehampton Road.

Will Shand, assistant head teacher of Highdown School, said: "One of the cranes that was working on the new building has collapsed and hit the other crane.

"We didn't actually see what happened but we heard the crash. One crane that was there is not visible now. The other one is crumpled."

He said 250 pupils and 85 staff were expected to move into the new building, one of the biggest special schools in the country, in September.

John Grevatt, 57, the caretaker at Highdown, said: "I heard a sound as if bricks were being loaded into a skip.

"I looked out and saw the two cranes tangled with each other and the red crane, with its broken jib, over the school building.

"It was lucky there were no pupils at our school today as staff were having an inset day.

"The children would have obviously been very concerned."

West Sussex County Council spokeswoman Jane Robinson said: "The crane came down within the contractor's site. It has not affected Durrington High School at all. All the pupils there are safe."

A Durrington High School spokeswoman said: "The school is operating as normal. We are all very busy making sure the children stay inside at the moment."

Ambulance paramedics, firefighters, police and Health and Safety officials were at the scene. Police sealed off the site and the main road leading to nearby Durrington station.

A West Sussex Fire Brigade spokeswoman said heavy rescue tenders had been sent from Worthing, Shoreham and Chichester.

A police spokeswoman said: "We believe there are injuries on the building site but no pupils have been hurt."

Police and safety officials were considering whether to evacuate nearby homes as there were fears the second crane might collapse.

Willmott Dixon spokesman Andrew Geldard said: "We are currently carrying out an investigation."

The accident comes less than a month after a giant crane toppled into the River Adur in Shoreham, trapping the driver.

He had to kick his way out of the cab window to escape when the arm of the 95ft crane fell as it was lifting roof trusses at the Berkeley Homes development at Ropetackle.