Utility crews are struggling to restore power to tens of thousands of people whose homes and businesses lost electricity when an ice storm walloped the Philadelphia region Wednesday morning.

Officials say the emergency operation could extend into the weekend.

After reporting as many as 623,000 customers were without power at one point, Peco apparently reached a tuning point in the afternoon. By 11 p.m., about 480,000 still lacked power as the utility wrestled with the worst winter outage in its history.

At one point, 87 percent of Peco's customers in hard-hit Chester County were in the dark, prompting officials to set up two shelters and a warming center for those in need.

In a briefing that started at 9:19 p.m., Gov. Corbett said the statewide total for utility customers still in the dark was 586,000, down from the day's peak of 849,000.

Corbett signed an emergency declaration for the five-county Philadelphia region and Lancaster and York Counties, which were the hardest hit by the ice storm. The declaration allows for the state to seek federal aid for the seven counties. He said 500 National Guardsmen had been activated and were ready to respond.

For those who were about to spend the first of what may be several nights in shelters, Corbett provided a list of what to bring along, including prescription medications and personal toiletries.

He also advised: "Please bring your patience. This may take a few days."

Montgomery County declared a state of emergency around 3 p.m. Wednesday. About 150,000 Peco customers - roughly half the county - were without power as of 6 p.m.

Earlier in the day, Corbett said five hospitals in Southeastern Pennsylvania had to rely on generators.

SEPTA Regional Rail operations also were slammed by downed trees, frozen signals, and power problems, with service suspended on four lines simultaneously during the day.

"We are looking at a multiple-day restoration effort," Cathy Engel Menendez, a Peco spokeswoman, said, warning the work probably would extend into the weekend. "We want our customers to understand that."

Peco was calling in crews from other utility companies to help.

Trees and wires already weighed down by snow from Monday's storm came down with the addition of rain and ice overnight, sparking the power outages.

The loss of electricity and road conditions prompted some schools and government offices in the Pennsylvania suburbs that had planned to open late to close for the day instead.

At least one serious injury has been reported. A man was critically injured by a falling branch in Narberth.

Villanova University announced that the campus would be closed through Friday because of the lack of power and heat. The university advised students living on campus, if they can travel safely, to go home.

Driving conditions are improving on major highways, though fallen trees, tree limbs, and wires are blocking many roadways. In Lower Merion alone, more than 60 roads were blocked or partially blocked by downed trees and tree limbs.

South Jersey was spared the brunt of the storm, with utilities reporting just 6,200 customers without power in Camden, Burlington, and Gloucester Counties.

"Camden County has dodged the bullet to a large degree," said Dan Keashen, county spokesman.

Here's the latest of what you need to know:

UTILITIES

Peco reports 479,526 customers are without power in Southeastern Pennsylvania: 118,901 in Bucks (a slight increase from the last report); 144,015 in Chester (a decrease of about 4,000); 53,206 in Delaware (a decrease of about 780); 150,565 in Montgomery (a slight increase); and 12,839 in Philadelphia (a decrease of about 1,270). At the height of the outages, at least 36 percent of Peco's 1.7 million customers in the five-county area were in the dark.

The record number of outages for Peco was 850,000, set during Sandy in 2012. The previous No. 2 was 549,100, set during an ice storm on Jan. 7, 1994.

Peco is strongly warning residents to stay away from all downed lines.

"Customers need to remember that any downed electrical wires, they should always assume that's energized and stay away from it - even if the power is out in the neighborhood," said Peco's Menendez.

Customers who lose power are urged to notify Peco by calling 1-800-841-4141.

In South Jersey, PSE&G reports 5,400 customers still without power in Camden and Burlington Counties. Atlantic City Electric has nearly 800 still waiting for power restoration.

At the high point, more than 61,000 were affected by outages across New Jersey, most of them PSE&G customers in Burlington, Mercer, and Middlesex Counties.

The State Police Headquarters and Office of Emergency Management in West Trenton were among those affected and had to operate on generator power.

MASS TRANSIT

SEPTA:

Regional Rail: Service on the Paoli/Thorndale Line is expected to remain suspended for the remainder of the day. Service on the West Trenton and Cynwyd Lines remains suspended until further notice. Riders on all other Regional Rail lines may experience delays of up to 30 minutes.

Norristown High Speed Line: Full service has been restored.

Trolleys: No current problems reported.

Bus: Service suspended on Route 120. Some routes are on detour. For more information: www.septa.org or follow @SEPTA on Twitter.

PATCO

No problems have been reported. www.ridepatco.org.

NJ Transit

Service restored on Northeast Corridor trains.

Cross-honoring of bus and train tickets is in effect.

AMTRAK

Service between Harrisburg and Philadelphia is suspended today. Dozens of trees are down on the tracks, Amtrak says.

DRIVING

Numerous accidents have been reported and a number of roads have been closed due to accidents, icing, or downed trees on both sides of the Delaware River, police say.

PennDot has lifted speed restrictions on regional freeways.

MAJOR INCIDENTS

A Narberth man is in critical condition after an ice-covered tree branch fell on him Wednesday morning while helping a neighbor deal with other fallen limbs, according to a borough official and neighbors.

The incident happened shortly before 8 a.m. near Shirley Road and Haverford Avenue, according to Narberth Borough Manager Bill Martin. The man, a doctor and father of two whose name has not been released, was taken to the trauma unit at the Hospital of the University of Pennsylvania.

AIRPORT

Some 115 flights to or from Philadelphia International Airport have been canceled, and 83 others were delayed, according to Flightaware. Check flight information at www.phl.org or www.flightaware.com.

Contributing to this article were Inquirer staff writers Joseph A. Gambardello, Jennifer Lin, Edward Colimore, Tricia Nadolny, Maria Panaritis, Jessica Parks, and Robert Moran.