More about it is reported here.

From the report, apparently the climbers met with the avalanche on their descent and K2 has the deadliest descent:

Those mountaineers who reach the peak have a much greater chance of dying while descending than on other peaks: 27 per cent have perished making their way back down – a rate three times higher than on Everest.

This is a real tragedy, and I express my deepest condolences to the families of the climbers – and lets all also pray for the best for the climbers who are still on the mountain fighting for their lives.