A garbage truck caught fire inside the O'Neill Tunnel Thursday afternoon, forcing the closure of the southbound side of Interstate 93 and spewing billows of smoke that could be seen for miles.

State transportation officials said shortly before 4 p.m. that two lanes were open on the road, which had been totally blocked for a period of time. The right lane remained closed near exit 23.

Boston Fire Department spokesman Steve MacDonald said crews responded to the fire near Exit 20 around 1:15 p.m. The fire began in the cab and spread to the back of the truck where the trash is located, MacDonald said.