Four Spaniards went missing on Sunday after scaling the 8,068-metre (26,469-foot) Gasherbrum-I peak in the Karakoram range, Manzoor Hussain, chief of the Alpine Club of Pakistan that coordinated the expedition, told AFP.
The climbers are Abel Alonso, from Pontevedra; Álvaro Paredes, from Valladolid, and Xevi Gomez, de Sarriá de Ter from Gerona, according to Spanish news agency EFE.
All these climbers are very experienced according to the Javier Garrido of Aragón Aventura which organized the expedition.
"We came to know about the four missing Spanish climbers today due to communication problems," Hussain said.
Anwar Ali of Lela Peak Expedition, the company running the trip, told AFP that one of the climbers had managed to make it back to base camp but the other three were still missing.
Hussain said search teams and other members of the expedition were looking for them.
"They have requested a search helicopter, but the weather is bad today and tomorrow also," he said.
"The chances of a helicopter search and rescue mission tomorrow (on Wednesday) are slim."
The missing Spanish climbers are part of a group of eleven mountaineers, most of the Spanish.
Three Iranian climbers went missing on another mountain last week and rescuers had called off the search for them, but at the insistence of the Iranian embassy another search effort was mounted on Tuesday, Hussain said, but to no avail.
The Iranians sent a distress call just after reaching the summit of the 8,051-metre Broad Peak on July 16.
"Today a helicopter was sent again on the mission but it could not find anyone and returned due to bad weather," Hussain said.
Pakistan is home to five of the world's 14 peaks over 8,000 metres, including the world's second-highest mountain, K2, but conditions are harsh and deaths not uncommon.
Last month Pakistan suspended expeditions to its second-highest peak Nanga Parbat after Islamist gunmen shot dead ten foreign trekkers.