Marine experts have been deployed to the Western Isles to try to prevent a mass stranding of pilot whales.
A Scottish SPCA spokesman said the first estimate was that between 60 and 70 whales had been spotted off the coast of South Uist, near Loch Carnan, and a large number appeared to have head injuries.
Volunteers from the British Divers Marine Life Rescue (BDMLR) travelled overnight in an attempt to reach the mammals.
The Scottish SPCA's senior inspector Calum Watt was making his way from the mainland to assist them.
If any of the whales in the group are unwell they could try to beach themselves and the others are likely to follow.
A spokesman for the animal welfare charity said: "One of our senior inspectors is on his way to the scene now. We are assisting the BDMLR with their operation."
At the end of October last year, a pod of pilot whales were in danger of becoming stranded in the same sea loch.
After being monitored closely by the coastguard, BDMLR and the Scottish SPCA, they moved safely back to sea.
But less than a week later a pod of 33 whales - believed to be the same group - were discovered dead on a beach in Co Donegal.
The Scottish SPCA spokesman said: "If they are sick they will try to beach themselves, and the healthy ones will follow.
"There is a worry that they could move on and turn up somewhere else. We are going to do all we can to make sure that doesn't happen."
Alistair Jack, BDMLR's Scottish co-ordinator, said: "We first became aware of the incident late yesterday and have immediately responded.
"We anticipate having trained medics and rescue equipment on the scene by mid morning. This is one of the largest events of this kind ever in the country."
Mr Jack said arrangements are being made for other sets of specialised rescue equipment to be flown to the island to assist with the rescue attempt.