It happened on Peters Drive in Brentwood around 11:15 a.m. Thursday.
Flames could be seen shooting from the roof and spread through the home.
A neighbor, 16-year-old Star Grant, ran into the basement of the house to get out her neighbor, 69-year-old Catalina Segura Jose.
"I knew she was down there and I was screaming for her and she was responding and I just ran downstairs and I got her," Grant said. "She didn't want to leave because all of her belongings were in there like her social security, everything. She was trying to grab everything and I said 'no, we have to get out now.'"
"She got me out," Segura Jose said.
Assistant chief Andrew Renison of the Brentwood Fire Department says when firefighters arrived, they noticed the relief valves on some propane tanks in the back of the house were released indicating they may have become too hot.
"That was happening until we got the tanks cooled off and we were able to get them removed from the actual house that was on fire," he said.
It's not yet known if they might have been tampered with.
Firefighters continued to put out hotspots into the afternoon.
"We had a collapse of the roof on the second floor. So we're going to be here for a little bit, extensive overhaul due to the conditions on the second floor," FDNY Asst. Chief Andrew Renison said.
Apparent house explosion causes large fire throughout Suffolk County home
The Red Cross is helping three families as a result of the fire. Resident Sandro Romero says that eight people live there.
He happened to be at work when the explosion happened. His wife called him to tell him what happened.
"My wife is really nervous and crying," Romero said.
The cause of the fire is preliminarily believed to be from the propane tanks.
The Suffolk County Arson Squad is investigating.
SUFFOLK NEWS: Off-duty firefighter rescues man from burning car in Ronkonkoma
Off-duty firefighter rescues man from burning car in NY
----------
* More Long Island news
* Send us a news tip
* Download the abc7NY app for breaking news alerts
* Follow us on YouTube