MOSCOW -- Six people were missing on Friday after their vehicles plunged into the Lena River in Siberia during a collision between a Russian ferry and a barge.

The Emergencies Ministry said the collision occurred at about 2 A.M. in Ust-Kut district, north of Siberia's vast lake Baikal. The missing drivers had been in their cars aboard a second barge being towed by the ferry.

"The collision was so violent that four cars and two trucks tumbled off the barge Sedelnikov into the river," a ministry spokesman said by telephone. "Six people, who were almost certainly sleeping in their vehicles, are missing. A rescue operation has been launched. We cannot say whether they are alive."

River transport is frequently the sole means of transporting cargo to remote areas of Siberia and Russia's far north, where roads often do not exist, Reuters reported.