Beachcombers found a dead porpoise with a savage bite mark washed up on the shore only a few miles from where walkers found a similar gruesome discovery the following day.

The twin finds at Winterton and Horsey, near Great Yarmouth, have led to speculation that sharks or a killer whale could be feeding off the north Norfolk coast.

Linzi Smith, 29, of St Nicholas Close, Long Stratton, took pictures of the mutilated porpoise when she and her fiance Steve Hunt, 36, came across it at Winterton on March 14.

But she only realised the discovery might be part of something more significant when she read a report in a national newspaper of a similar find at nearby Horsey the following day.

Miss Smith, an administrative assistant in Norwich, said: 'We love walking along the beach at Winterton because that is where we had our first date.

'When we spotted the dead porpoise it was a bit of a shock to the system. Close up, you could see its stomach was gashed open and there were obvious bite marks towards the tail as well.

'It was only when I visited my grandparents' a few days later and picked up their newspaper that I saw the details of the similar attack.'

Miss Smith said her fiance had two little girls and last year they had taken them to the beach at Winterton - the gruesome discovery had put the frighteners on her now and made her think twice about going near the water this summer.

Hollie Moran, 24, who found the dead porpoise with fresh blood being washed out by the waves at Horsey, was intrigued to be told of Linzi's earlier discovery.

She said: 'Two attacks so close together are quite scarey. We went bodyboarding at Horsey last year but I would think twice now this summer.'

Miss Moran, of Clay Road, Caister, was strolling on the beach with her boyfriend Tom Buy when they came across the 5ft porpoise with chunks taken out of its head and tail.

'It was brutal. When you zoomed in you could see it must have been a bite of about nine inches.

The latest discoveries come in the wake of mystery seal deaths off the north Norfolk coast last year, their injuries possibly put down to boat propellors.

Dr Ken Collins, a national shark expert at the University of Southampton, examined the pictures of the Horsey porpoise and concluded it was 'undoubtedly a shark bite', speculating it might be a shortfin mako.

However, EDP naturalist Percy Trett said the attacks were more likely to be the work of a killer whale.

He said: 'This kind of attack is unusual for our region. However, killer whales do occur off the Scottish coast and occasionally come down the North Sea. They will attack porpoises and seals.'

Mr Trett said although biting sharks occurred off other coastlines around Britain, such as Cornwall, there was no history of them off Norfolk.