Coastguards have warned North Norfolk holidaymakers to be wary of dangerous, powerful tides after two stranded teenagers were rescued from a sandbank at Wells.

Coastguards have warned north Norfolk holidaymakers to be wary of dangerous, powerful tides after two stranded teenagers were rescued from a sandbank at Wells.

The boys, aged 13 and 15, wandered on to exposed sands and were lucky to escape when they were cut off by the rapid flood tide last Wednesday night.

They were beaten by the force of the water as they tried to wade across a deep channel to safety, but were spotted by people in a nearby dinghy and brought ashore with the help of the inshore lifeboat.

Although disaster was averted this time, the stretch of coastline has seen similar instances in the past when casualties were caught out by the timing and ferocity of the tidal flow.

Last May, 12 teenagers on a fishing trip were plucked to safety after rising waters stranded them on a sandbank. And in July 2007, a 15-year-old Tamil boy on a pilgrimage to Walsingham was swept to his death by a strong outgoing tide while swimming near Wells lifeboat station.

Colin Tomlinson, rescue centre manager for Yarmouth coastguard, said the problems could also happen at remote beaches like Brancaster, Burnham, Moreston and Blakeney, which had no lifeguards and could be subjected to massive tidal changes.

"The north Norfolk coastline is a lovely area and we do not want to scare people," he said. "But it is very easy to wander out on to the sands and people need to be aware of what the tide can do.

"Parents need to be aware of tide times and check out the areas their children are playing in. They need to make sure they know what is going to happen and what to do if they get into trouble. Children should let someone know where they are going to be, and to not go to areas where no one else is around and where there is no mobile phone signal. Knowledge is the key. The sea is inherently dangerous and will catch you out if you are not careful."

Mr Tomlinson said high-spirited holidaymakers often ignored warning signs and were not aware the tide did not run uniformly. "It creeps in at first and then runs in the third and fourth hours," he said.

"If you get cut off on a sandbank, it is not advisable to walk into a deep water channel. It is better to signal for help, but if there is no one who can see you, these problems can happen."

Lifeboat volunteers advised holidaymakers to heed a warning siren which operates at Wells between 8am and 8pm from May to September. It sounds similar to an air raid siren, with two 25-second blasts given four hours before each high tide, warning people to return to the land side of the channel.

Peter Rainsford, chairman of the Wells Lifeboat Management Group, said: "The lads were lucky, they were quickly spotted by observant members of the public and they had the sense to stay where they were. The tide at the moment is extremely strong and should be treated with respect."