Officials issued a rare avalanche warning on Saturday for climbers at England's third highest mountain after strong winds created unstable stretches of ice and snow.

With up to half a metre of snow, freezing temperatures and gales, authorities said conditions at Helvellyn in the heart of the Lake District were the worst in 16 years.

The 950-metre peak is considered too dangerous even for experienced walkers, according to the Lake District National Park Authority.

"It is lethal underfoot as edges are literally breaking away," said Craig Palmer, the authority's fell-top assessor. "An added danger comes from a cornice of snow which could break off and avalanche at any time.

"I have rarely seen anything as bad as this in the Lake District and I would strongly urge people -- even those experienced in winter mountaineering -- not to venture out on to hills until the situation improves."

High winds have whipped up the snow, creating drifts that are only loosely attached to the mountainside.

The Met Office said the temperature on Helvellyn was minus 3.9 degrees Celsius, with wind chill of minus 15.9C.

"There is a high avalanche risk until the snow pack has time to consolidate," it said in a message on its Web site.

Helvellyn is one of the most-climbed peaks in the Lakes. It inspired the poets William Wordsworth and Walter Scott and has been painted by scores of artists, including John Constable.