A woman died Monday in a one-alarm fire that began on the second floor of a Haverhill townhouse, authorities said.

At 11:30 a.m., firefighters respond­ed to 41 Brickett Hill Circle, a two-story residential building with four units, the Haverhill Fire Department said.

A spokeswoman for Essex District Attorney Jonathan W. Blodgett said she did not expect the victim to be identified Monday.

The Haverhill fire and police departments are investigating the fire jointly with State Police assigned to the State Fire Marshal’s office and the district attor­ney’s office. State Fire Marshal Stephen Coan said the cause of the fire was being inves­tigated.

Coan said that the number of fire deaths in Massachusetts in January was unusually high, but that there was no single cause behind the deaths.

“This is the eighth fire death so far this year, which is a disturbing number to me,” Coan said. “It’s a high number, looking at historical trends. . . . It’s trending in the high side for fire deaths which normally occur during the month of January, but there is not a general commonality in the causes of the deaths.”

Coan could not immediately provide numbers on how many people died in fires in January last year. The state Department of Fire Services said there were 37 fire fatalities across the state for all of 2012.

Coan said fires in winter months are often caused by heating and electrical systems that are overburdened as residents try to keep warm.

He also said investigators were looking at whether the townhouse had working smoke alarms. “It’s an important part of every investigation that we do,” Coan said.

The death came just a day after a Gloucester woman died in a two-alarm blaze in her home at 4 Windsor Lane. The cause of the Gloucester fire and the identity of the victim are still under investigation, accord­ing to the district attorney’s office.