KATHMANDU (AFP) - Former Gurkha soldier Nirmal Purja remains on target to conquer the world's 14 highest mountains in a record-breaking seven months despite death-defying queues on the biggest peak of them all.

Waiting for more than seven hours last week to get to the top of Everest and then back to the safety of his camp - in a pile-up that he documented in a photo that has gone viral - injected doubts into Purja's minute-by-minute strategy.

"My plan was to climb Everest and Lhotse as fast as possible, breaking my own previous record but that day, I was stuck in traffic," Purja told AFP back in the comfort of Kathmandu.

In 2017, the ex-British special forces member climbed the two mountains in a record 10 hours and 15 minutes.

"I sat four hours on the way up and three and half hours on the way down and that kind of made me (worry) like I won't be able to achieve the record," he said.

In the end, the phenomenal 35-year-old climber completed the 8,848m Everest, Lhotse at in 48 hours and 30 minutes, according to his backup team.

Also a record: he tackled the three peaks in five days.

SPEED CLIMBER

This season, Purja has climbed six mountains above 8,000m in 31 days.

But the jams on Everest have been blamed for at least four of the 11 climber deaths on the peak.

The iconic photo Purja snapped of the queue of mountaineers leading up to the summit has triggered calls for better management of the crowds and screening of climbers to avoid fatalities.

"Of course there are certain worries - you are cold and you cannot move," said Purja.

Other climbers said that some of those who attempted to climb Everest were grossly unprepared.

Nepal issued a record 381 Everest permits this season and a short weather window resulted in some teams waiting several hours in the "dead zone", running out of oxygen and risking fatal exhaustion.

Purja was better prepared.

A teenager when he joined the British Gurkha service, he was inspired to start Project Possible by his 2017 climbs.

But tackling the world's 14 highest mountains in seven months was radically ambitious. Purja says he will complete the mission by November.

In the 1980s, it took Polish climber Jerzy Kukuczka seven years, 11 months and 14 days to climb the 14 peaks.

South Korean climber Kim Chang-ho managed the feat in about a month less without supplemental oxygen.

"When I first said I would climb all 14 highest mountains in seven months, everyone said it was impossible. I am doing this to prove the power of the concept of possible," he said.

Purja is to leave for Pakistan within a week to climb the next five mountains, including K2 and Nanga Parbat, while raising funds for his expeditions. He expects his next climb to start in June.

"I absolutely believe I am one in eight billion people who can do this... in terms of decision-making ability, stamina, endurance. everything," he said.