A badly hurt Czech climber and 16 members of his party are trapped on the slopes of a volcano in Russia's far east.
A helicopter which tried to reach the group was forced back by bad weather and fog.
The alarm was raised by three members of the party who managed to get off the volcano and alert the emergency services.
The Klyuchevskaya volcano, on the remote Kamchatka peninsula, is active and suffers rockfalls, earthquakes and gas escapes.
But the 4,750-metre (15,700-foot) peak remains a popular destination for climbers, who try to reach the top to peer into the crater.
Kamchatka's volcanoes remain popular challenges for climbers
Officials say the injured climber is believed to have suffered serious head injuries.
They have criticised the group for attempting to scale the volcano without the help of local guides.
The party are thought to be trapped in two groups, with one party 4,000 metres
(13,000 feet) above sea level and the other group lower down the mountain.
The rescue helicopter has returned to the base of the volcano and is waiting for better conditions.