The NI Everest team with sherpas

Expedition leader Richard Dougan called colleagues in County Down on Wednesday after reaching the 6,400 metre mark.

Mr Dougan said temperatures fell below -15 degrees at night.

He said the expedition team was holding up well and were not affected by high altitude sickness, which caused two members of the group to drop out last week.

Three of the team plan to ascend to Everest's North Col on Thursday.

They will sleep there for one night as part of the acclimatisation process before the assault on the world's highest peak.

On Wednesday the expedition sherpas climbed to the North Col, fixing tents, stoves, fuel and other supplies.

The team leader said they remained on schedule for a summit attempt in mid to late May.