Three climbers died on Everest over the weekend and another is missing, officials confirmed on Monday, in one of the deadliest episodes on the peak since an avalanche swept through base camp and killed 18 two years ago.
More than a dozen climbers have been rescued from the 8,848 metre (29,030 feet) mountain in the last three days after running into difficulties on the world's highest peak, helicopter rescue operators told AFP.
The weekend fatalities appear related to altitude sickness and bring the death toll to five during a season marked by unpredictable weather, strong winds and unusually cold temperatures.
The weather calmed over the weekend, opening a narrow window for climbers to make a bid for the top.
Despite the large numbers crowding towards the peak, there have been no reports of long queues.
Over a hundred climbers are expected to attempt to summit from Nepal's south side on Monday before the weather changes in the next few days and brings strong winds, according to forecasts. 
"Today there might be as many at 150 climbers reaching the top from the Nepal side, but it isn't a record number," Ang Tsering Sherpa, head of the Nepal Mountaineering Association, told AFP.
In 2012, 255 climbers summited from both sides of the mountain in a single day, Sherpa said.
Slovak climber Vladimir Strba was found dead on Everest on Sunday, a few hundred metres from the summit, Kamal Parajuli of Nepal's Tourism Department confirmed.
He was above the 8,000 metre mark -- known as the mountain's "death zone" -- when he died, an area that also claimed the life of American climber Roland Yearwood on Sunday.
The death zone is notorious for its difficult terrain and thin air, where low levels of oxygen heighten the risk of altitude sickness.
Ongoing search
An Australian climber died on the Tibet side of the mountain, local media reported, quoting the Tibet Mountaineering Association. 
The 54-year-old from Queensland was reportedly hit by altitude sickness after reaching 7,500 metres and died as he was trying to descend. His name has not yet been officially released.
A fourth climber has been missing since Saturday when he lost contact shortly after reaching the summit. 
His Nepali guide managed to reach Camp 4, just below 8,000 metres, but sustained severe frostbite. Officials originally said he had been found unconscious. 
A search is under way for the climber, who is from India's northern state of Uttar Pradesh, but authorities at base camp were unable to contact the rescue team on Monday.
Legendary Swiss climber Ueli Steck died in late April while on an acclimatisation climb, and 85-year-old Min Bahadur Sherchan perished in May while attempting to reclaim his title as the world's oldest person to summit Everest. 
More than 120 climbers have successfully summited Everest from the south side so far this season, with another 80 reaching the peak from the Tibet side.
Hundreds are still waiting to summit before the monsoon arrives in early June, marking the end of the short spring climbing season.
Last year Everest claimed the lives of five climbers, while a total of 640 people summited from both sides of the mountain.