THEY have razor sharp claws, voracious appetites, are capable of laying up to a million eggs and can signal environmental disaster for riverbanks and flood defences.

The march of the exotic Chinese mitten crab is unrelenting. Spreading from the estuaries of China's Yellow Sea, it has already invaded the US and Europe.

Now the crabs, named for the dense patches of hairs on the claws of larger juveniles and adults, have been sighted in the North-East.

Worried ecologists yesterday reported the first sightings of the Chinese mitten crab (Eriocheir sinensis) in the River Tyne, prompting them to make an urgent appeal to people who spot them to report the locations.

Newcastle University scientists made the appeal as they began charting their progress and started groundbreaking research into their breeding patterns, in the hope of stemming their advance.

The creatures, accidentally introduced to Europe from the Far East through ships' ballast, burrow into river banks - up to 50 holes per square metre - causing them to collapse.

This poses a severe threat to flood defences that could ultimately have a devastating impact on homes and businesses in the region.

It is also reported that, in their native Far East, they are host to a lung fluke which infects humans as a final host - which can lead to tuberculosis-like symptoms.

The Tyne's ecological system is also at risk as the predatory mitten feeds on protected species such as the native white-clawed crayfish and salmon eggs and fry.

The crab can cross land and migrate almost 1,000 miles.

Dr Matt Bentley, of Newcastle University's Department of Marine Sciences and Coastal Management, said: "There is a huge potential for damage to the rivers in the Northern region as there are relatively few physical barriers to stop the crabs burrowing into the banks.

"Nobody has yet realised the extent of the damage the mitten crab can do.

"We are asking everybody to look out for the mitten crab and to report any sightings."

Student Leif-Matthias Herborg, who is completing a PhD on the crab, said he hoped to find out more about its reproductive biology to help combat the problem.

He said: "We know that other crustaceans, including some crabs, use chemical messages, such as pheromones, to attract the opposite sex.

"What we hope to do is find out if they use this system and, if so, develop pheromones to entice them into traps."

Anyone who spots the crab should call 0191-222 6660 or e-mail leif-matthias.herbor