BOSTON -- A winter storm pounded New England with pouring rain, sleet and ice, knocking out power to roughly 350,000 customers in Massachusetts, closing schools and roads and prompting Gov. Deval Patrick to declare a statewide state of emergency Friday.

IMAGES: Ice Storm Downs Trees, Power Lines

The storm, which began Thursday night, coated trees with ice, causing branches to break onto power lines and roadways throughout central and western Massachusetts. By Friday, emergency crews raced to clean up the debris, but homes, businesses and even some courts in Worcester remained dark and officials warned it could be days before power is restored.

"All of the resources at our disposal have been made available to try to get the roads clear and power restored," said Patrick, who declared the state of emergency and called up 500 members of the National Guard to help clean debris and clear access to downed power lines. "The earliest estimates that we have for power being restored is Monday, and I think many of us view that as an ambitious estimate at this point."

"This is a really extreme situation we are experiencing," said Jackie Barry, a spokeswoman for National Grid, which had about 297,000 electric customers without power, mostly in the Worcester area and Merrimack Valley.

The hardest hit community was Leominister where 44,000 were in the dark. In Worcester, 40,000 were without power and 43,000 customers in North Andover had no electricity.

NStar, which serves mostly eastern Massachusetts, reported scattered outages of 7,000 customers. Eastern and southeastern Massachusetts, where temperatures were significantly higher, were getting rain and the National Weather Service declared a flood warning.

Western Massachusetts Electric Co. reported nearly 18,000 customers without power. Some towns, including Becket, Windsor, Cummington and Middlefield, are experiencing near blackout conditions.

"Stay home if you live in Holden, don't come to Holden if you work here," Holden fire Chief Jack Chandler said.

The entire town is without power and some senior citizens on oxygen have been transported to either the hospital or a shelter opened at the town's senior center.

The nearby town of Sterling has canceled school and is also asking residents to stay off the icy roads.

"It's terrible out there," police Chief Gary Chamberland said. "The main two arteries through town are impassable. We can't even get emergency personnel to work."

The town has opened an emergency shelter at a local school.

Ice collected on tree limbs, weighing them down until they snapped and came down on power lines, Judge said. The transmission lines themselves are also being iced up, Barry said. She warned against approaching downed lines, even if they don't appear to be live.

The Massachusetts Bay Transportation Authority reported delays on some commuter rail lines to clear fallen tree limbs from the tracks.

It could be days before some customers have power restored, Barry said.

"Some high-voltage lines affected are on rural rights of way in remote areas and we're not sure if we can even get to them," she said.

Eastern and southeastern Massachusetts, where temperatures are significantly higher, are getting rain and the National Weather Service has declared a flood warning.