Iris Carey, 4, and Violet Carey, 51/2, died in the 1:41 a.m. explosion that spared their parents while they all slept in the same second-story bed. Heath Carey crawled out of the rubble and pointed rescuers toward his wife, Tara, and their daughters trapped in the 65 Main St. building.

Investigators said it is likely a gas leak sparked the fatal blast, but said they are not ruling out any possibilities. Authorities said a gas leak was reported on the west side of the building shortly before the blast. The explosion generated some smoke, but little fire damage.

"We're going to be looking at everything. There was the odor of gas upon arrival. It's one of the things the fire marshal will look at," Hopkinton Fire Chief Gary Daugherty said. "We haven't ruled out anything at this point in time. It's an open case right now."

State police Sgt. Martin Foley said a defective electric line or a pilot light could spark a gas explosion.

"You gotta have fuel. Gas is a fuel, and it needs some sort of igniter," he said.

Crews used a front-end loader to remove the remains of the home from the street and pull an almost empty oil tank, used to heat the building, from the basement. Investigators dug by hand to remove a second oil tank and a gas appliance.

NStar spokesman Mike Monahan said no one was working on the gas line to the home and he is not aware of any problems. Others, however, said there may have been some problems with the gas line.

The little girls' grandmother, Cindy Germain, said NStar crews were in the area just a few weeks ago. Tony Defreitas, who escaped with his family from a third-floor apartment, said the gas bill he received last week was abnormally high.

"My gas bill was very high. It's usually $15-$20, but this time it was $45," he said.

Defreitas, his 5-year-old son, Brian, and pregnant wife, Poliana Compos, were sleeping in two back bedrooms at the time of the explosion.

"The whole house was shaking. I thought it was a thunderstorm," said Defreitas, 32, wearing borrowed sweat pants and slippers. "My wife fell down and I fell over her. My little boy was screaming in his room. I went to my boys' room and the bed was on top of him."

Defreitas and Compos, wrapped in a blanket, crawled out of their third-floor kitchen window with Brian behind them after police officers broke it open. They walked onto the street and were taken to MetroWest Medical Center in Framingham with minor cuts, authorities said.

Compos, nine months pregnant, was due to deliver the couple's son, Ryan, yesterday, Defreitas said. The 20-year-old did not have the baby, according to a spokesman from MetroWest Medical Center, but was expected to spend the night for observation.

Another man who also lived on the second floor, 37-year-old Richard Maijs, was not hurt.

Janet Webster, 47, and her children, 25-year-old Emily, 15-year-old Hayley and 19-year-old Matthew, were in a car across the street from their first- floor apartment when she called 911 on a cellular phone, authorities said. They were not hurt.

Janet Webster declined to speak to a reporter when approached at the scene of the blast.

A dispatcher at state police headquarters on Rte. 9 in Framingham picked up the call and transferred it to Hopkinton fire, where it was answered at 1:41 a.m.

"She said she thought she heard something coming from the basement and she thought she smelled gas," said fire Lt. Stephen Slaman, who took the call.

The house exploded just as Slaman hung up the phone and sounded an alarm, he said.

"It sounded like the biggest lightning bolt ever," he said. "It actually popped out a couple of windows." The fire station was just two doors away.

The American Red Cross assisted families at the scene of the blast and set up many with food, clothing and temporary shelter.

Hopkinton resident Leonard Pearson has owned the building, registered in the assessor's office as a three-family home, since January 1974, according to town records. It is assessed at more than $200,000.

Pearson declined comment when approached by a reporter at the scene of the explosion. He could not be reached for comment later in the day.

The force of the blast blew out the walls of the balloon-construction building, built in the 1890s, and sent the roof onto the sidewalk. The windows of nearby businesses were shattered and residents more than two miles away felt shock waves.

Main Street from Rte. 85 to Pleasant Street was closed all day.

"I thought I was dreaming or something," said Peter Marso, whose apartment above Star Package Store is across the street.

"I thought it was a big thunderstorm. It was a big boom."

Kathy Dragin, who lives two miles away, said the explosion woke her and her husband from a deep sleep.

"It sounded like lightning hit our house. It sounded like a bomb," said Dragin, a friend of the Webster family. "My husband kept walking around the house. He kept thinking something hit the house."