AMESBURY — Firefighters from three communities yesterday morning battled a one-alarm fire that reportedly began in the rear of a ranch-style house on Pond Hill Road.

Amesbury fire Chief Jonathan Brickett said a motorist called authorities on his cell phone around 10:30 a.m. after seeing smoke coming from the area. By the time firefighters arrived, the back portion of the house at 6 Pond Hill Road was already enveloped with heavy fire.

"It had already broken through," Brickett said.

Assisting local firefighters were units from Salisbury and Merrimac. Newburyport fire Chief Stephen Cutter was also present. Police officers closed off the entrance to Pond Hill Road from Route 110 (Haverhill Road) near the Merrimac line.

Brickett said firefighters attacked the fire from both inside and outside the building. A ladder truck was stationed directly above, allowing firefighters to spray water very close to the fire's core.

The house is owned by Linda Baldinelli and is currently occupied by her son, Robert Mazalauski. No one was home at the time of the fire, Mazalauski said.

As firefighters began checking for hot spots and removing charred debris from the back of the house, friends and family members comforted a visibly shaken Mazalauski as snow fell at a heavy clip, accumulating on the heads and backs of those huddled around him.

Brickett said he has an idea how the fire started but couldn't offer a definitive cause, saying it was still under investigation. Amesbury police Sgt. Glenn Chaput, Detective Sean Leary and other members of the city's fire investigation squad arrived around 11:30 a.m. Building inspector Denis Nadeau was also on hand to assess the condition of the building.

Newburyport and South Hampton firefighters covered the Amesbury station until firefighters returned shortly before 1 p.m.