A shark may be responsible for the deaths of 45 porpoises off the North-East coast, marine experts have warned.

An investigation has been launched after the porpoises - many with chunks ripped out of them - were washed up along the coastline in recent weeks.

Decapitated seals have also been found, together with the remnants of large fish.

After examining the kills, marine authorities say a Mako shark may be responsible.

The Mako shark, which is considered dangerous, can swim up to 60mph, is five to eight feet long and weighs about 1,000 lbs.

Marine medics and staff from Sunderland Lifeboat Station, were called to Seaham beach, County Durham, on Friday and Saturday, as reports of dead porpoises were received.

Ron Carroll, from the station, said: "The first porpoise had a chunk taken out of the side of its head and neck. The bite mark was about ten inches long.

"While on Saturday, the next porpoise had been bitten on the left side of the fin and its abdomen and this was about 12 inches across.

"There is speculation now that it might be a shark, possibly a Mako shark."

An autopsy on the porpoises is being carried out by the Natural History Museum in an effort to find out what killed them.

A spokesman for the Humber Coastguard said that it had not received any reports of shark sightings, but he added: "There are sharks out there."