More than 200 mountaineers ascended Mount Everest on Wednesday, setting a new record for the highest number of climbers to stand on top of the world in a single day. 

A staggering 250 climbers had started from Camp IV, at 7,900 metres, on Tuesday night, hoping to reach the top of Everest by Wednesday morning, with just a week remaining before the Spring ascent window closes. 

But conditions were exceedingly favourable on Tuesday night and Wednesday, leading to a 24-hour window—the longest ever single-day weather window in history—and what has been called a ‘marathon climb’.

More than 200, but not all 250, are reported to have made it to the top. Exact figures will only be available once the climbers descend to Base Camp.

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“Details of all the successful climbers have yet to arrive, but based on our inquiries of various expeditions, more than 200 climbers have made it to the top,” Gyanendra Shrestha, the government liaison officer stationed at Everest Base Camp, told the Post in a phone interview.

Mountaineer Alan Arnette said in a blog post on Tuesday that there could be as many as 250 people going for the summit on Tuesday. “Teams have been leaving the South Col every hour since 1500hrs,” he wrote. 

“As the weather was favourable all day, the expedition was never-ending. The climb may have ended at 3:00 pm,” said Shrestha. “Walkie-talkies and satellite phones aren’t working, so we don't have the exact details yet.”

With so many vying for the peak, a veritable ‘traffic jam’ occurred on the slopes, but no casualties have been reported.

[Read: Exactly how high is Everest? Nepal says it will announce next year.]

According to Shrestha, many climbers who reached the South Summit area at 8,690 metres, just below the Hillary Step—a vertical rock face with a sharp slope, which many say is not there after the 2015 earthquake—on early Wednesday morning complained of waiting for more than two hours in queues to climb.

Heavy traffic poses potential risks for climbers if the weather suddenly takes a turn for the worse. Traffic jams are dangerous as climbers are exposed to thin air and many could run out of oxygen during the final phase of the ascent. They have to wait long hours for their turn to reach the top, as well as to make it down from the summit.

In 2012, around 260 climbers had made their final push for the summit, but only 179 had successfully made it to the top due to a small weather window. That year, four climbers died of exhaustion and altitude sickness while descending from the summit.That record was broken on May 19, 2016 when 204 climbers scaled the peak.

This season, the Everest climbing season started on May 14, with a team of eight rope-fixing high-altitude climbers opening up climbing routes. The first two-day weather window closed on May 16 after over 150 climbers made it to the summit. The second climbing window opened on Monday, May 20.

[Read: Kami Rita Shrestha scales Everest, second time in a week, to take his record tally to 24]

According to Shrestha, more than 150 climbers are still waiting at Camp IV, hoping to reach the summit on Thursday morning. As of Wednesday, nearly 400 climbers had reached the summit this season alone, said Shrestha.

According to the Department of Tourism, 381 individuals have been cleared to climb Everest this spring season. As each climber hires at least one climbing guide, the total number of ascents may reach a thousand, the department has estimated. For the past three years, the success rate on Everest has been close to 70 percent.