She spotted the woman's body and went in to the water to drag her on to the beach at Barton on Sea in Hants.

The RNLI at Mudeford in Dorset launched its Atlantic 85 class lifeboat at 2.45pm but attempts to resuscitate the woman failed.

Her rescuer was then taken to hospital with shock and hypothermia.

Debbie Doe, RNLI spokeswoman, said: "Another lady went in to assist the casualty and to pull the body ashore. She then suffered from hypothermia and shock."

A Hampshire Police spokeswoman said: "Police are not treating her death as suspicious and are carrying out inquiries to ascertain her identity but a post-mortem is unlikely to take place until tomorrow."

Coastguards alerted the RNLI and police after the body of the woman, believed to be middle aged, was seen in the Solent off Marine Drive by a passer-by walking on the beach.

A Portland Coastguard spokesman said the two women were not known to each other.

"She (the rescuer) was part of a small group of people who were on the beach," he added.

He said the sea was "choppy and rough" at Barton on Sea in New Milton today.