MADRID (AFP) - A police helicopter flying to rescue a mountain climber with a broken ankle crashed in Spain on Sunday, killing all three crew members on board, emergency services said.

The helicopter's blades struck the side of a mountain close to the Picos de Europa range in the northwestern province of Leon. The aircraft then slid down the rock face, regional emergency services said in a statement.

Two Guardia Civil pilots and a member of a mountain rescue team died in the accident, it said.

A fourth member of the rescue team who had already exited the helicopter to search for the injured climber sounded the alarm, a spokesman said.

Emergency services, including three helicopters and an ambulance, were dispatched to the scene and found the bodies of all three men.

The injured climber was transported to hospital by another police helicopter.

Funeral services for the three policemen will be held on Monday at the cathedral of Leon, the provincial capital.

Prime Minister Mariano Rajoy said he was "shocked" by the "tragic accident" and offered condolences to the family and friends of the three men.

In a statement Rajoy said their "heroic sacrifice in the line of duty fills us with pain" even as it "redoubles the admiration, pride and gratitude we feel towards those who are committed to the noblest of tasks: saving people's lives".

The cause of the accident is under investigation.

Spanish media reported that the area was engulfed in fog at the time but Interior Minister Jorge Fernandez Diaz ruled out inclement weather as a cause.

"Weather conditions were perfect. These things unfortunately happen when you work in risky conditions," he told reporters in Leon after meeting with local officials.

The Picos de Europa range, although not the highest in Spain, is a favourite among walkers, trekkers and climbers.

It is considered to be one of Europe's most challenging mountain ranges, with changable weather and treacherous terrain full of chasms and gorges.