With crews on the ground unable to find her, the police helicopter found the woman with only her head visible above the rising water - just half an hour after a desperate call for help from her family.

The daring rescue attempt took place after the family of the woman, who had entered the river close to Crab Marsh, called police at around 8.25pm.

Ambulance crews, the fire service, Spartan Rescue and a duty officer from the port were all scrambled to the scene, but they could not see her or identify where she may have entered the water.

With the tide rising, officers in the helicopter used its infra red technology to locate a heat source from the river bed. When the helicopter located the woman at 9pm only her head was visible above the rising water.

The helicopter crew landed on the bank next to the woman, threw her a rope and pulled her free, where she was then taken to hospital for treatment.

Ch Supt Andy Hebb said: "This was a co-ordinated, successful, effort to find a vulnerable person which demonstrates the value of having this aircraft.

"With the tide rising fast, without the swift actions of the helicopter crew using their overhead view to full advantage, we would not now be talking about a successful rescue, but an unfortunate tragedy.

"When the helicopter landed, only the woman's head could be seen, with the rest of her underwater and stuck in the mud.

"I'm sure the two officers and pilot who conducted this rescue would say they are only doing their job, but this was police work at its best. They should be very proud of their actions."