Lacey Gallagher, 18, a senior at Little Flower Catholic High School for Girls, was killed and six other young Philadelphians were seriously injured in a one-car crash on the Pennsylvania Turnpike in northern Bucks County shortly before 3 a.m. yesterday, state police reported.

The seven had left a Little Flower prom in Center City and were on their way to the Poconos for the post-prom weekend, said Donna Farrell, spokeswoman for the Archdiocese of Philadelphia.

Neither the unidentified 17-year-old driver nor any of the passengers was wearing a seat belt, state police said.

The northbound lanes of the turnpike's Northeast Extension were closed for about three hours between the Lansdale and Quakertown interchanges during the accident investigation.

Four of the victims, including Gallagher, attended Little Flower, and news of the accident stunned their fellow students, Farrell said.

The school opened the chapel during the day for grieving classmates.

"They were crying and crying," said Farrell, adding that 20 to 25 were there when she visited. A prayer service is planned for 8 p.m. today at the Holy Name of Jesus Church at Berks and Gaul Streets.

"The community of Little Flower Catholic High School for Girls is devastated by this tragedy, and our hearts go out to the family of Lacey Gallagher," the school's president, Sister Donna Shallo, said in a statement.

The 2001 Suzuki XL-7, a seven-passenger SUV, was heading north in the left lane when it hit the concrete median in Milford Township, Trooper Richard M. Johns reported. It spun across its lane, rolled over several times, and landed on its roof in the right lane, facing north, Johns reported. Six occupants were thrown from the vehicle.

Gallagher was pronounced dead at the scene by Bucks County Deputy Coroner Jeffrey A. Naugle, the state police report said. Gallagher's family declined to comment yesterday evening.

The other passengers were Katelynn Brooks, 18, Patrick Shiffler, 19, and three 17-year-olds who were not identified because they are juveniles, state police said.

Three of the injured were sent to Lehigh Valley Hospital in Allentown and three to St. Luke's Hospital near Bethlehem.

Contact staff writer Walter F. Naedele at 610-701-7614 or wnaedele@phillynews.com.