MANCHESTER, N.H. (WHDH) - Investigators are searching for the cause of a massive fire that broke out in Manchester, New Hampshire on Monday.

Four people were killed, including two young boys.

People who live in the area are remembering those lost, as news of the tragedy continues to sink in.

A memorial continues to grow outside the scene of the fire as they try to understand how the fire happened.

“I heard popping, banging sounds,” said Maryrose Donohue, who called 911. “I opened the curtains in the office and I thought I was going to see fireworks.”

The fire started just before 5 a.m. Firefighters raced to the scene on Wilson Street, but it was too late.

Two of the victims were found dead inside and two more were pronounced dead at the hospital. All four victims were in the same apartment on the second floor.

This is the deadliest fire in New Hampshire since 1983. Thirty other residents were displaced by the fire.

“I still can’t believe it happened, I’m still trying to get it to sink in, even though I’m sitting here staring at it,” said Jimmy Day, the victims’ best friend.

“My prayers and thoughts go out to the families of the deceased,” New Hampshire Governor Maggie Hassan said. “As always, this is a really important reminder of how fragile life is.”

The victims’ names are not being released. Autopsies will be conducted on Tuesday.

The building was last inspected on Dec. 17, 2015. The building inspector said all units in the building had working smoke detectors and there were no complaints on file about the building.

Investigators were on the scene for hours, trying to identify a cause.

They will return to the scene Tuesday.

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