Dozens of mountaineers have converged on Pakistan's mighty K2 peak, vying to conquer one of the world's last major climbing challenges -- reaching the summit in winter.

Four teams with around 60 climbers and sherpas between them have begun climbing the world's second-highest peak -- known as the "savage mountain" -- where winds can blow at more than 200 kilometres per hour (125 miles per hour) and temperatures drop to minus 60 degrees Celsius (minus 76 Fahrenheit).

Since the first attempt in 1987-1988, only a handful of winter expeditions have been made on the 8,611-metre (28,250-feet) mountain in the Karakoram massif on the Chinese border. None of them have got above 7,650 metres.

Even in summer, almost one in six climbers who attempt the summit die, and since the first success in 1954 only 450 people have managed it -- compared to more than 6,000 who have scaled Mount Everest. 

Lockdowns and travel bans sparked by the coronavirus outbreak mean the summer climbing season last year was a washout in Pakistan and other popular climbing destinations in the region, such as Nepal.

"People had plans for the year but they couldn't go anywhere," said Dutch mountaineer Arnold Coster, who is helping to lead one of the expeditions. "So we've been kind of jobless for a year and now lots of people want to do something," he told AFP.

Although Pakistan is still battling more than 2,000 fresh coronavirus cases a day, the country has reopened. 

Throughout December, the teams flew into the northern town of Skardu and trekked over the Baltoro Glacier to reach base camp, from where they will begin the ascent -- an expedition that could take up to two and a half months in total depending on the weather.

- Egos and avalanches -
K2 is set amongst some of the most breathtaking landscapes the world has to offer -- and some of the most dangerous.

"Multiple factors must fall in line for anyone to have a chance of summiting," said climbing coach Alan Arnette, who points to altitude sickness, avalanches and landslides -- as well as egos -- as potential pitfalls. 

Coster's expedition, organised by Nepalese company Seven Summit Treks, stands out with its supersize team of around 20 clients of varying experience and around 30 support staff. 

Together, they will have to accommodate differing ambitions, including those who do not want the help of sherpas or oxygen. 

"We have a lot of different people with different ideas. For us, as leaders, it's difficult to manage. But from a manpower point of view, if people work together, we have a bigger chance," said Coster. 

Climbers spend days going up and down attaching ropes to the mountain to help them reach the top and also acclimatise to the thinning air -- particularly tiring work for small groups.

One trekker has already been airlifted from base camp because of a pre-existing health condition, the company said. 

- Concerns of crowding -
Mingma Gyalje has climbed 13 of the highest peaks but failed to reach the K2 summit last winter. 

This year he is heading an all-Nepalese team of three experienced sherpas.

Gyalje is a contender to summit this time, better prepared for the cold after his harsh lesson last year -- but concerned about sharing a crowded mountainside with other teams. "I don't feel like it's a good sign having so many people, too many clients," he told AFP.

"It puts pressure on the staff. Because there are people in the team who don’t want to go back without reaching the summit."

Many mountaineers shared the same concerns, fearing some of the climbers are not sufficiently prepared. 

Of the other two expeditions, one is led by Nirmal Purja, a star Nepalese climber and former British special forces serviceman who has set his team of six apart with a plan to paraglide off the summit. 

In 2019, Purja scaled all fourteen of the world’s 8,000-metre mountains in six months and six days -- however, that was in the summer.

The fourth team is an Icelandic-Pakistani pairing of three. 

With so many people on K2 this winter, the chances are good that at least one person will reach the top, said Arnette, the climbing coach. "However, almost everything must go practically perfect," he said.

"And that rarely happens on an 8,000-metre peak, much less on K2."