Coastguard teams have confirmed that the oil has impacted quite heavily on bathing beaches

David North, Holyhead Coastguards

"Within one bay of the coastline there's between five and five-and-a-half tonnes of this oily substance," said Holyhead Coastguard David North .

"We wouldn't advise going on the beach at the moment because of the amount of this stuff laying about.

The area affected stretches from Carmel Point to Point Lynas on Anglesey.

"Coastguard teams from Moelfre, Penmon and Cemaes, as well as the Moelfre Inshore Lifeboat have been out to investigate the situation and have confirmed that the oil has impacted quite heavily on bathing beaches," Mr North added.

"They have taken samples of the oil and these will be taken for chemical analysis. Local authorities and the Environment Agency have also been informed and are monitoring the situation."

The samples have now been sent to the Maritime and Coastguard Agency's laboratory in Edinburgh.

It is not known when the results of tests are expected.

The responsibility for any clear-up operation along the shore would fall to the local authority.

Both Anglesey Council and the Environment Agency are aware of the incident.

The oil is not thought to be crude oil but some sort of lighter oil but it is not yet known exactly what the substance is.