Local radio said 18 people were believed to have died and 50 were trapped in the tunnel in an area where hundreds of small illegal mines have been in operation for decades.
"They could be dead because it happened last night," Franco Tito, a village chief, told radio interviews. He said a powerful explosion was heard before the tunnel caved in.
Police said they were investigating the cause of the blast. Rescue helicopters could not reach the site due to bad weather, said Antonio Cloma, a disaster official.