Fears were growing last night for the safety of a Limerick mountaineer and up to five of his colleagues after they were hit by a river of ice as they descended the second highest mountain in the world, K2.

A rescue attempt was continuing in an attempt to locate Gerard McDonnell (37), from Kilcorman, and his fellow climbers on one of the world's most treacherous mountains.

He had earlier celebrated making it to the peak of K2 with a group of Dutch explorers at approximately 3pm Irish time on Friday.

McDonnell's friend and fellow adventurer Pat Falvey told the Sunday Tribune that up to 12 climbers appeared to have been hit by a river of ice from a serac, or large column of ice, as they descended the mountain in an area known as the Bottlekneck.

It is understood that their ropes were cut as a result of the incident.

Falvey said that the whereabouts of at least three of the group are unknown, although it is thought that as many as six people could be missing.

He confirmed that the wife of one of the men, a Norwegian, had reported seeing him being carried away by the avalanche along with three or four others. McDonnell's satellite phone had been located.

Falvey said a serac is like a "leaning tower of Pisa" where the ice can break off and descend down the mountain.

Forty nine climbers have died on K2, with 22 of these deaths occurring while descending from the summit.

However, Falvey said it was possible that the group had managed to get onto another route, although they had not been spotted on this route as of last night. McDonnell, a vastly experienced mountaineer, had previously attempted to climb to the summit of K2 in July 2006.

But after reaching 8000m he and his fellow climbers had to abandon the attempt when a number of the team they were climbing with got altitude sickness.

K2's summit is 8611m and it is known for weather which is significantly colder and more unpredictable than Mount Everest.

Located on the Chinese border with Pakistan, it was first scaled in 1954 by two Italians — Lino Lacedelli and Achille Compagnoni.

Since then there have been 189 summits, compared with around 1,400 on Everest.

McDonnell's most recent dispatch from his website, dated 25 July, said it had been agreed that the weather forecast on 1 August is, for the most part, "equally as good" as the day before.

"That'll give the lead party a buffer if there are any delays. The following days appear to be more than adequate for a safe descent," it states.

"Let luck and good fortune prevail !!! Fingers crossed. Sin é anois a chairde. Ta an t-am ag teacht."

Mountaineering experts last night stressed that the rescue effort was ongoing, and that details of what had happened were "sketchy" at times.

Updates

However, various international mountaineering websites were providing updates as to the situation on the mountain.

One of these, k2climb.net, said that while the group was descending "a big chunk of ice fell from the serac below the summit, taking a large part of the fixed lines with it.

"This is a serious situation," it stated. "Good news is that previous fatal accidents on K2 were more often results of avalanches, sudden storms or disorientation before actual deterioriation."