CHELMSFORD, Mass. (WHDH) -- Two people were killed in a Chelmsford apartment that was destroyed by fierce flames Saturday night.

Building four of the Woodcrest condominiums caught fire around 11 p.m. Saturday. The chief said the blaze started in a 3rd floor condo.

“You could see the flames shooting so high,” said a neighbor, Carol Cartier.

Six people were in that condo; a couple believed to be in their 70's and their kids and grandkids, visiting from out of town.

The smoke alarms alerted the fire department and others in the building.

Paula Telesco lives down the hall and said she also heard someone screaming.

“I heard him saying something like, 'I can't find them' and I thought to myself, ‘Oh my God, this is not a false alarm,’” said Telesco.

The fire marshal said the older couple in that condo died in the fire.

Their 7-year-old grandson was airlifted to a Boston hospital with severe burns and the other three members of that family were also taken to the hospital with less serious injuries.

A few other residents waited on their balconies until firefighters arrived.

“There were a couple people hunkered down, I kept telling them, wait for the ladder, wait for the ladder,” said Chief Michael Curran, Chelmsford Fire Department.

Once Telesco saw the thick black smoke seeping into her apartment, she bolted.

“I didn’t grab my purse, my phone. When I saw that smoke, I thought, this is the stuff that kills you,” said Telesco.

When residents returned in the daytime, they saw the front and the damage didn’t look that bad, but when they walked around back, they realized why the fire department is calling this a total loss, and why this building will have to be torn down

“And then we walked over and I was like ‘Oh my God, it’s completely gone. The fireman said, ‘your apartment is gone.’ I said 'gone?'” said Telesco.

Investigators haven't released the exact cause, but said it doesn't appear to be suspicious.

“We are focusing on several accidental scenarios,” said one official.

Twenty condos are now gone. Dozens are left looking for a new place to stay after losing everything.