The mammal, which is thought to be a minke whale about three metres, 9ft, long was spotted by workers at a petrochemical plant near the mouth of the River Carron at 9am on Tuesday.

It became stranded but was freed by the rising tide with the help of INEOS workers, who managed to keep it alive by hosing it with water then digging a channel so it could swim free.

Rescuers, including specialists from the British Divers Marine Life Rescue (BDMLR), were on alert in case the whale became beached again when the tide went back out.

Kirsten Harper, a medic with the BDMLR, said the whale first became beached opposite North Shore Road in Grangemouth, near where the River Carron meets the Forth Estuary. It was last seen swimming towards the River Carron.

Miss Harper, who is based at the Scottish Sea Life Sanctuary near Oban, Argyll, said: "The whale was first spotted at 9am by workers and we were alerted to attend.

"It stranded itself on the mudflats at the docks. On-site it was hosed it as it needed to be kept moist, not being submerged, and it re-floated when the tide came in early in the afternoon.

"The whale managed to swim away, but we are concerned that it is not out of trouble yet and it may beach again when the tide goes out."

A spokeswoman for the Scottish SPCA, who also attended the rescue, said: "We were alerted to the whale, which was stranded for a time but managed to get free after the high tide.

"It hasn't been seen since around 2pm. There is concern that it may come back in, but we won't know until the tide goes down again. For the moment, we are hopeful that it won't be back."

A spokesman for Falkirk Council said: "Emergency planning officers were in attendance at Grangemouth docks to see if they could be of assistance. They were on standby and to observe, but the heroes of the hour were the BP and Ineos staff who hosed the whale down and helped it to swim away."

A spokesman for Ineos said: "The Ineo emergency response team went to the mammal and sprayed it with water to keep it wet. The tide came in and it was able to swim off."