Four boys who were rescued by a helicopter after getting stuck in mud were lucky not to have died, says a coastguard.

The 12-year-olds were winched to safety from the beach at Warden Point in a three-hour rescue on Sunday night.

Sheppey coastguard's deputy station officer Tim Judge said the friends had been cut off by the tide.

"They all had mobile phones but three had dead batteries. One had just enough power and he had the presence of mind to ring 999. If he had had a dead battery as well I don't know what could have happened.

"It was a close run thing - the water was around them.

"It could have been a tragedy. They could have been stuck there."

The SOS call was made at 9.30pm but the boys could not describe exactly where they were.

They were found after a joint search by the Sheerness inshore lifeboat and eight Sheppey coastguards, who were on land.

Neither could reach them so they had to call in the RAF.

Mr Judge said: "The helicopter winched them up and deposited them at Warden Springs holiday camp and passed them into our care.

"I've never seen people so muddy. One of them had lost both shoes.

"They had been staying at Shurland Dale Holiday Park and were attempting to get back there.

"What they were doing out on their own at that time I don't know."

The boys were cold and frightened but otherwise unharmed, said Mr Judge, and their parents were called to pick them up.

He warned people to avoid the cliffs, particularly after the recent bad weather.

"The bottom of the cliffs are absolutely treacherous," he said.

"With all the rain and erosion we've had it just turns all the mud into quicksand.

"Do not go near the cliffs and definitely not the bottom."

The rescue, which took until after midnight, was the 29th callout for the island's coastguard this year.

Mr Judge said the total was similar to the number dealt with by this time last year.

In 2011, the coastguard responded to 126 calls for help, which was a record.