PELHAM, N.H. (CBS) – Investigators are trying to figure out what caused a huge fireworks explosion at a home in Pelham Tuesday night that left 11 people hurt, including five children.

Police and firefighters were called to Chris Pappathan’s house on Dodge Road around 7:30 p.m. shortly after the blast and fire on his back porch.

An aerial view of the back porch of the Pelham home after the explosion Tuesday night.

Six adults and five children were injured. Among them were Pappathan and his grandson, according to a neighbor.

Three of the children are still being treated for severe burns at Shriner’s Hospital for Children in Boston. Two adults also remained in the hospital Wednesday.

Neighbors told WBZ-TV Pappathan, an insurance executive, had a large amount of fireworks at his home because he hosts a display for the neighborhood every year.

Amateur fireworks are not illegal in New Hampshire.

But something went wrong at the start of Tuesday’s event where about 50 people showed up to watch.

“Every year it gets larger and larger,” neighbor Barbara Catanzano told WBZ. “He’s very careful, very cautious, knows what he’s doing, but something didn’t go right.”

“I do believe a firework was set off and spun onto the deck and set off some of the others that were standing by,” neighbor David Cook  said.

Cook told WBZ his eight-month-old granddaughter was flown to Shriners Hospital with burns to ten-percent of her body.

His daughter is being treated at Massachusetts General Hospital with a severe burn on her chest.

“Get help! Get help! That’s all we heard,” neighbor Jackie Troy told WBZ.

“We got all our chairs out and we’re all sitting there. We got a little granddaughter that got very emotional over it. She heard everyone screaming. She started really bawling, so we had to get her in the house.”

Police removed more than 90 boxes of fireworks from the home Wednesday. (Photo by Lauren Leamanczyk)

Police searched the home Wednesday and removed more than 90 boxes of fireworks from the home.

The state fire marshal has also joined the investigation.