Massachusetts State Police detectives assigned to the Suffolk County District Attorney’s Office, together with investigators from the Chelsea Police Department and State Police Troopers assigned to the Fire Marshal’s office, continue to investigate the facts and circumstances of a fire that occurred in a five-unit apartment building at 295 Spruce Street in Chelsea at about 11:30 p.m. last night.

Upon arrival at the scene, State Police detectives assigned to the Suffolk DA’s office observed extensive damage to the interior and exterior of the building. Two women and one man were transported to area hospitals for treatment. One of those women, a 20-year-old Chelsea resident, was pronounced dead of her injuries at the hospital. An autopsy to determine the cause and manner of her death will be conducted.

A 33-year-old male victim sustained severe burns and remains in critical but stable condition. A 26-year-old female was treated for minor injuries and released from the hospital.

The investigation into the cause and the nature of the fatal fire remains active, authorities said. State Police assigned to the Suffolk DA’s office investigate all unattended deaths in Chelsea, Revere, and Winthrop with the assistance of local police. Members of the State Police Crime Scene Services Section also responded to assist.