An 84-year-old man rescued from his burning North State Street house Friday died at Massachusetts General Hospital from his injuries. The Attorney General’s office is investigating the cause of the blaze, which burned a duplex across the street from the state prison.

Robert McMillan, who owned the duplex at 282-284 N. State St. since 1989, was discovered in his bed, and pulled out minutes before firefighters were ordered to evacuate the building. An ambulance initially took McMillan to Concord Hospital, but he was later taken by MedFlight to Boston, where he was pronounced dead.

According to Lt. Ken Kiehl of the Concord Fire Department, the dramatic fire traveled quickly through the house, built in 1880. A prison guard noticed flames and called the fire department at about 11:30 Thursday night; by 12:36, the building had become so unstable that firefighters were ordered out.

“We had heavy fire shooting through the roof,” Kiehl said. “The house is probably a total loss.”

The Concord Fire Department initially responded to the call. Subsequent alarms at 12:30 drew firefighters from Allenstown, Boscawen, Bow, Canterbury, Chichester, Epsom, Loudon, Pembroke, Hooksett, Manchester and Penacook Rescue to the scene. The Webster, Pittsfield, Loudon and Hopkinton fire departments covered Concord fire stations. At 12:43, the fire department issued a general call, and drew more volunteers from around the city.

Fire Marshal Tim McGinley said it took until about 4:30 a.m. to get the fire under control.

“It was a very stubborn fire. . . . These old New England homes,” he said.

McGinley said the snow, which fell steadily yesterday morning, slowed his crew’s investigation. The Concord Fire Department, Concord Police and the State Fire Marshal are now investigating with the Attorney General.

“We’re still, in some sense, beginning our investigation,” he said yesterday evening more than 12 hours after the fire had been extinguished.

The Concord Red Cross responded, and ultimately paid to put up three neighbors who had been evacuated from the house next door. Firefighters were concerned that the house, which was only 15 feet from McMillan’s home, might catch fire.

Tag Truesdale, the Red Cross emergency services director, arrived on the scene around 1 a.m. He said that a caretaker traveled to the hospital with McMillan, though he did not believe the caretaker had been inside the house at the time of the fire. Kiehl said that he believed that a man who took care of McMillan lived on the other side of the duplex, though he does not think he was at the house when it caught fire. Kiehl could not confirm whether he traveled to the hospital with McMillan.

The numerous fire trucks blocked North State Street until about 6 a.m. and the police allowed traffic to move slowly through narrow lanes for most of the morning.

The police are asking anyone with information relating to the fire to call the Concord Police Department at 225-8600. Callers who wish to remain anonymous may call the Concord Regional Crimeline at 226-3100.