A rescue operation is under way after approximately 100 seabirds were washed up on the south coast covered in an unidentified sticky white substance.
The Royal Society for the Protection of Birds (RSPB) said the guillemots, a kind of awk, were discovered on Lyme Bay near Weymouth.
They have been taken to West Hatch Animal Centre in Taunton but attempts to clean them have been hampered by not knowing what the substance is, Grahame Madge, of the RSPB, said.
"At the moment, the best guess is there are around 100 birds ashore and there are concerns the birds are affected in as widespread a region as from Cornwall to Sussex so we could be dealing with quite a large incident as all these birds could be proved to come from the same pollution incident," he added.
"We are urging the government to identify the source of the pollution and the pollutant."
Mr Madge said 25,0000 guillemots were using the stretch of coast.
The rescue operation is being run by the Royal Society for the Protection of Animals (RSPCA).
Mr Madge said: "The area is of international importance for the seabirds.
"It is likely that a larger number than we have seen could be affected.
"The RSPCA are having difficulty with the clean up of the birds.
"With oil you know what it is and how to deal with it but the unidentified substance is hampering efforts."
The RSPCA said many of the birds, which were "mainly being found near Portland, west Dorset", had "very sore legs" but there was no number for how many had died.
Peter Venn, manager of RSPCA in West Hatch, Somerset, said: "The numbers of birds arriving in to our centre are growing and we are doing all we can to help them - but it is too early to tell how successful these attempts will be.
"We do not know what this substance is or where it has come from yet but we do know it is not fuel.
"It may be bi-product from manufacture, but at this stage we just do not know.
"We would urge anyone who finds any of these birds to contact the RSPCA on 0300 1234 999.
"There are also reports of the sticky substance washing up on the beach, so we would urge people walking their dogs in the area to also be careful."
A spokeswoman for the Maritime and Coastguard Agency said: "We have received reports of seabirds being washed ashore covered in a white waxy substance, from Cornwall to Portland, Dorset.
"We are liasing with the RSPB, RSPCA and Natural England to find out the extent of the problem and, if at all possible, to determine the source."
Dorset County Council warned members of the public about handling distressed birds on the south coast.
"During the past 24 hours, a number of live birds have washed up on beaches covered in an unknown substance," a spokesman said.
"Staff from the RSPB, RSPCA and Dorset Wildlife Trust have been working to take the birds into care and clean them up ready to be released into the wild.
"While the substance is being identified, agencies are urging people to avoid coming into contact with the birds and to keep pets away from the shoreline."