Specialist divers battled yesterday to rescue three cavers trapped for four days deep underground in the Pyrenees mountains of southwest France.

The cavers, two French and one Greek, were mapping the Romy chasm, a mountain cave 700 metres underground, when a sudden rise in water last Wednesday blocked their only way out.

Around 20 rescuers, including divers, explosives experts and porters, began a descent into the cave yesterday, hoping to reach the tunnel behind which the cavers are trapped by the evening.

Once the teams have reached the entry to the passage, four divers from French Cave Rescue (SSF) will try to get through the flooded tunnel, which is only 50 centimetres high in places.

They hope to make contact with the trapped cavers, give them food and assess ways of getting them out.

A spokesman for the local fire and rescue service said the divers would reach the area where the cavers are trapped by 10 p.m. at the earliest.

A dozen-strong rescue team went down last Thursday to try to blast open a seam directly above the trio to evacuate them through the cave roof, but rising waters made the operation impossible.

Eric Soupra, who is leading the rescue efforts for the fire service, said the cavers were unlikely to be freed from the cave before late this evening at the earliest.

Dominique Beau, the head of SSF, said the return of cold weather to the area could make the rescue easier, as it would lead to a fall in the level of underground water.

The trapped cavers, aged around 35 to 40, were part of a seven-member group from a club based in Lille, northern France, that began mapping work last Monday and planned to resurface last Thursday.

The other four cavers were in a different part of the cave when their colleagues became trapped, and returned to the surface last Friday.