Pakistani authorities believe that two mountaineers, a Spaniard and an Argentinian, missing for over a week in Pakistan's northern Himalayan mountains perished in an avalanche, officials said on Sunday.

Alberto Zerain Berasategi from Spain and Mariano Galvan from Argentina were last heard from on 23 June while at the 6,100 metre base of Nanga Parbat, the world's ninth-highest mountain, said Karrar Haidri, spokesman for the Alpine Club of Pakistan.

"The spot they were believed to be in has been struck by a large avalanche and the helicopter rescue officials have said (survival) appears unlikely," Haidari said.

Haidari confirmed that search and rescue operations were called off on Saturday.

Both men were experienced climbers with Zerain being part of an elite club to have scaled the world's two tallest mountains, Everest and K2.

Galvan climbed Everest in 2012 but an attempt to climb K2 alone and without supplemental oxygen ended at 7,300 metres.

Muhammmad Iqbal, owner of Summit Karakorum, the tour company that arranged the climbing expedition, said the last helicopter search found no trace of the men, adding that another climbing team started its ascent of 8,126 metre Nanga Parbat on Sunday.

Pakistan rivals Nepal for the number of peaks over 7,000 metres (23,000 feet) and is home to the world's second-tallest mountain, K2, as well as three others which are among the world's 14 summits higher than 8,000 metres.

Nanga Parbat was the scene of an attack in 2013, when gunmen dressed as police officers shot 10 foreign mountaineers and a local guide at the 4,200-metre base camp.

The killings were claimed by both the Pakistani Taliban and a smaller group of Islamist militants.

Since that attack, the number of expeditions has dwindled, wrecking communities dependent on climbing tourism for income and depriving Pakistan's economy of much-needed dollars.