FITCHBURG, MASS. (WHDH) - Firefighters battled a massive blaze in Fitchburg that residents say began with an explosion Sunday night, with firefighters rescuing residents during the fire.

Residents said the fire began shortly before 6 p.m., with one couple saying they heard an explosion on the third floor like “a giant cannon” going off and another person confirming a huge bang.

“It sounded like a giant firework went off just behind us,” one man said.

‘I looked up and a window pane hit me in the head,’ another woman said.

Resident Jillian Gould said firefighters rescued a woman from a third-story window after she was prepared to jump from the flames.

“We saw in the third floor window a lady push out an air conditioner and going to jump out, the fire department was telling her ‘don’t jump, don’t jump,'” Gould said.

“We had heavy fire up on the top floor, the crews did a good job of getting everybody out,” said Fire Chief Kevin Roy.

Firefighters said no fatalities were reported although one person was not accounted for. Several people were taken to the hospital with heat exhaustion and smoke inhalation.

Some pets were trapped inside the building, residents said.

Displaced residents were gathering at St. Anthony Church, and the Red Cross was on scene to provide help.

Firefighters are still investigating the cause of the blaze.

This is a developing news story; stay with 7NEWS on-air and online for the latest details.

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