THE three-man crew of the Kent Air Ambulance were killed last night when the helicopter ploughed into power lines and crashed in woodland.

In a separate incident a man and a woman also died when a two-seater plane crashed in a cornfield, police said.

The Jodel light aircraft crashed close to an equestrian centre near Alton, Hampshire, and was seen plummeting to earth, said a spokesman.

The victims of the air ambulance crash were said to be the pilot and two medics who had been called out to the scene of a road traffic accident.

But the helicopter plunged into woodland and crashed near the M2 motorway outside the village of Burham, near Rochester, Kent after the crew were turned back from their emergency mission.

The helicopter had just taken off from Rochester Airport, where it is based.

A police spokeswoman said the crew had been called off after it was discovered they were not needed at the crash and were returning to the airfield.

All three victims are men, but further details have not yet been released.

The helicopter crashed at an isolated spot off a road called Common Road, about half a mile from the motorway.

''The call came in at 5.39pm from a member of the public who saw it coming down,'' she said.

Electricity company Seeboard said the helicopter crashed after flying into power lines.

Air accident investigators will be examining whether the air ambulance could have been in trouble before colliding with 11,000-volt overhead power cables.

One conductor was brought down by the crash, causing a black-out in an area around Rochester Airport. Alternative supplies restored electricity within 50 minutes.

A joint statement issued by the Kent Air Ambulance Trust and the Kent Ambulance NHS Trust said: ''This has come as a great shock to us all. We have lost three exceptional men in tragic circumstances.

''At this time our thoughts are very much with their families.''

One witness said there was little sign of wreckage, only a blackened circle where the helicopter smashed into the ground, apparently in a fireball.

The man, who declined to be named, said: ''There appears to be little left of the helicopter. There is a doctor examining the scene to search for the remains of bodies.''

Yesterday afternoon, the helicopter and crew visited the

Medway Valley Park complex in Strood on a publicity trip to raise urgently-needed funds.

A spokeswoman from the Virgin cinema at the complex said the crew had been handing out balloons to youngsters.

Police said an emergency call was sent to the crew about a serious road accident near Cuxton on the A2.

After it became clear that its support was not needed, it continued back towards its base.

Shortly afterwards, at about 5.39pm, it hit overhead power cables, fell to the ground 6 metres below and burst into flames.

Police were unable to confirm reports that the ambulance did not normally fly at weekends because of a lack of funds.

Jim Smith, chief executive of Kent and Canterbury Hospital said: ''We are devastated by the accident. It's just unbelievable, absolutely dreadful. They are a vital part of the emergency services and give themselves unselfishly to others. Our hearts go out to their families and relatives.

''There will be great sadness at the hospital tomorrow. Our accident department people in particular know them very closely.''

Health Secretary Frank

Dobson was being kept informed of developments, said a spokesman for the Department of Health.

''He is very concerned and will get a full report first thing in the morning.''

An air exclusion zone is in force around the crash site area and a large section of woodland is sealed off.

The helicopter was French-made and purpose-built as an air ambulance. A leading air ambulance fundraiser in the area said she was ''devastated'' at the deaths of the men.

Mrs Doreen Northover, 55, the postmistress at Burham, lives in the Bluebell Hill Valley just below Rochester Airfield where the helicopter was based.

Mrs Northover has a collection tin in her shop to raise money for the air ambulance and at Christmas helped organise a disco to raise money for the helicopter and the crew.

Mrs Northover said she was used to hearing the helicopter every day over the village.

She said: ''They are brilliant, I just feel devastated. I can't speak highly enough of them. I used to see them every day and it was reassuring to know that they were there. They were close to everyone's hearts.''

Police said the plane that crashed in Hampshire was thought to be heading towards nearby Lasham and had put out a mayday call shortly before crashing.

The spokesman said the pilot and passenger had died instantly.

The plane crashed 200 yards from the farm of Irish international show jumper Peter Charles.

Mr Charles, 39, said: ''We were just returning form a show and I happened to glance up. I noticed the plane gliding, there was no noise coming from it so the engine must have stopped.

''It looked as if the pilot was trying to straighten up to crash land in the field but it was obvious he wasn't going to make it.

''The plane started corkscrewing and hit the ground with a terrible thud, there was no explosion. The whole thing lasted about 10 seconds.

''I ran over to see if I could help the people in the plane while one of the lads from the stable called the emergency services.''

A police spokeswoman added: ''It is clear that the pilot was experiencing difficulties before the accident.

''He said he was going to land at a nearby airfield but unfortunately he was unable to reach it.''

The Department of Transport's Air Accident Investigation Branch has begun an inquiry.