According to the Chinese Central Television broadcaster, rescue services managed to identify 9 out of 13 victims.
Earlier, eight deaths were reported.
The Public Safety Bureau of Medog county received an emergency alert on Tuesday evening. An avalanche blocked the entrances to the tunnel on the highway connecting Medog and Mainling counties. People and cars were trapped inside the blocked tunnel.
Rescue work is ongoing. According to television, 696 rescuers with 236 transport and specialized vehicles are working at the site.