Thick plumes smoke rose in Berlin early Saturday morning from a large fire that burned for hours, injured firefighters and destroyed several businesses.

The unstable building hung over Main Street by the evening with damage so extensive that investigators may never know how the fire started, WMUR News 9's Aaron Kellogg reported.

Firefighters from four towns worked from sunrise to sunset at two buildings on Main Street, which authorities closed after the fire ignited at about 5 a.m. Authorities said the road would likely remain closed all day.

The fire ravaged at least two buildings through the 9 a.m. hour The roof and third floor were completely down by the time firefighters gained control of the fire by 11 a.m.

WMUR News 9 has learned that fire officials believe the fire may have started in a second-floor apartment. The fire destroyed several businesses and offices, including Dave's Music Mania; Louie's Barber Shop; Home Sweet Home, an apartment management company; Profile Electronics and the Berlin office of Rep. Paul Hodes, D-District 2.

Crews swapped out from time to time to allow firefighters to warm up amid subzero conditions. A thermometer display on a bank sign in town showed a temperature of negative 19 degrees.

Kellogg reported that the temperature hovered around 27 below zero when the flames started -- so cold, that a fire hose ruptured.

Two firefighters were injured during their work. A hose struck one firefighter, causing broken bones, and another firefighter suffered a shoulder injury. Their identities were not immediately released.

The state fire marshal's office continued to investigate late Saturday as crews prepared to reopen Main Street, but firefighters used so much water that the street was covered with ice. Some of the fire hoses were buried in ice and crews had to chisel them out.