ISLAMABAD, August 3, 2008 (AFP) - At least seven mountaineers died near the summit of K2 when a huge chunk of ice sheared off the mountain and hit them, and several more climbers are missing, Pakistani tour operators said Sunday.

Three South Korean and two Nepali climbers were among those killed when the disaster struck on the notoriously treacherous Himalayan peak, the world's second highest mountain after Mount Everest.

'According to latest updates I can confirm seven casualties,' Mohammad Akram, vice president of the company that organised one of the expeditions, told AFP.

'There are reports of nine casualties, but I cannot confirm it yet.'

Akram said five climbers from the Dutch-led NoritK2 expedition his Adventure Foundation Pakistan organised were still missing.

He said the group was hit by the falling ice as they made their descent on Friday and an air search had been called in to try to find the missing climbers.

The avalanche apparently struck an area of the mountain known as the 'Bottleneck,' where the South Korean and Nepali climbers died.

'Three Koreans and two Nepalis have died at Bottleneck,' Ghulam Muhammad, owner of tour operator Blue Sky Trekking and Travel told AFP. 'The liaison officer at base confirmed the casualties.'

K2, which sits on the border between Pakistan and China, is notoriously difficult to climb. Weather patterns in the high-altitude Karakorum range where the mountain is placed are also extremely volatile.

The extent of the casualties was still unclear Sunday, with Spanish media reporting up to 11 people may have been swept away by the avalanche, citing a blog linked to an 18-member expedition.

Basque daily Gara quoted Basque climber Alberto Zerain as saying he had reached the summit of K2 on Friday evening but a 'drama' had hit several members of his expedition.

NoritK2 expedition leader Wilco van Rooijen, from the Netherlands, was spotted late Saturday returning, but climbers Gerard McDonnell from Ireland and Hugues d'Aubarede from France were missing, as was Pakistani porter Karim, Akram said.

Italian climber Marco Confortola had also returned and was suffering from frostbite on his arm, he said.

Nazir Sabir, a leading Pakistani mountaineer told private Geo television that Rooijen was rescued by his fellow climbers and was injured.

Separately, government officials said late Saturday that the Serbian mountaineer Dren Mandic and another unidentified member of his expedition died after falling into a crevasse on K2 last month.

Deputy Commissioner of Skardu town Wazir Ishfaq told AFP the Serbs, who began their climb in June, had informed the authorities of the two casualties on their return.

K2, known in the local language as Chogori or King of Mountains, has a ratio of climbers to deaths of 27 percent, three times that of Everest.

Italian climbers Achille Compagnoni and Lino Lacedelli first scaled the mountain on July 31, 1954.