They might be among the most appealing of baby animals. But conservationists are warning sightseers to keep their distance from seal pups on East Anglia's beaches, after fears some have already been killed by those who have strayed too close.

Grey seals breed around The Wash and Norfolk's coastline from late November.

By New Year, there are large numbers of young in colonies at Horsey Gap and Blakeney Point.

Young seals grow rapidly but are completely dependent on their mothers for the first weeks of their lives.

Getting too close can cause the females to abandon their young, which may then perish.

David Wood, the National Trust's head warden for the north Norfolk coast, said: 'For most of the year you can get within 50 or 100 yds if they're hauled up on the sands and if you get too close they'll just scurry off into the water.

'But seal pups can't swim for the first three or four weeks of their lives so you can walk up to them and that can be construed as they're not bothered.'

As well as driving away the mother, male seals can crush pups if they become agitated.

'They're a species you can get close to and get some great views of but you don't want to get too close,' said Mr Wood.

As Horsey's seal colony has grown, more and more visitors have been attracted to see the animals.

Along the coast at Blakeney Point, there are record numbers of pups.

Jim Temple, who has run boat trips to observe the animals for 50 years at Blakeney, said: 'They've been seriously on the increase for the last 10 years.

'A fortnight ago the wardens that come now and again to monitor them counted 700 pups and they're still having them now.

'Last year there were 600 pups, the year before 480 and the year before that 370.

'These grey seals are multiplying very, very well but I think they do have an effect on the common seals because they eat all the food. Seven hundred pups means 700 mothers.'

Blakeney's seals are not as vulnerable to disturbance, as they breed in a remote area of the point which is a long walk.

But Mr Temple said: 'They don't worry about us because they're used to boats but people walking on the beach shouldn't go near them.'

Wardens from the Lincolnshire Wildlife Trust have warned people to stay away from the seals at Donna Nook, near Skegness, after a six-fold increase in pup deaths.

Staff at the RSPCA's Norfolk Wildlife Hospital at East Winch, near King's Lynn, are currently caring for 41 seals.

Centre manager Alison Charles said: 'There's a really good team of volunteer wardens at Horsey who keep an eye on the beach and don't bring pups in unless they need to be.'

Populations of both grey and common seals, which breed in the summer, are still recovering from an outbreak of PDV (phocine distemper virus) six years ago, which wiped out almost half of them.