At least 40 people are missing in a blizzard on the frozen tundra of Russia’s Yamal peninsula, a news agency reported Thursday.

Four vehicles - including a bus with 30 people aboard - left Tuesday from the town of Labytnanga, near the Arctic circle some 1,400 miles northeast of Moscow, the ITAR-Tass news agency said.

They were headed for Muzhi, 150 miles across the tundra. On the same day, three vehicles set out from Muzhi to meet the convoy, ITAR-Tass said. By Thursday, there was was no word from either group, it said.

Officials believe the two convoys may have become lost in a blizzard.

A rescue caravan was organized to trace the route, ITAR-Tass said. A helicopter was standing by to help, if the weather permits, it said.