The Canberra public servant ended what had been an extremely anxious wait for his supporters by declaring last night he had reached the true summit of Mount Shishapangma in Tibet late on Friday afternoon.

There had been fears for his safety after he failed to make contact through the weekend.

After making his safe return to base camp, he posted on his website last night that he had fulfilled his long-held ambition of climbing the world's 14 mountains that are higher than 8000m.

''Very tough climb via a variation of the Inaki route on the north face, caught in a storm on descent with an open bivouac at 7600 metres without equipment thrown in for good measure. Just into base camp now, bit tired, more later,'' he wrote.

Earlier yesterday fellow climbers had expressed concern for the welfare of Lock and his climbing partner Neil Ward.

Quoting experienced American mountain guide Dan Mazur, website mountaineering.net reported a ''huge storm'' enveloped the mountain on Friday morning the same day Lock was to attempt the summit.

Lock planned to spend Thursday night at camp three (7400m) before attempting a difficult route to the mountain-top.

It is unknown where the 47-year-old was situated on the mountain when the weather deteriorated.

For more, pick up a copy of today's Canberra Times