(Adds details on injuries, comments from governor, dateline)
By Elizabeth Daley
MURRYSVILLE, Pa., April 9 (Reuters) - Twenty people were injured, at least nine seriously, when a student at a Pittsburgh-area high school went on a stabbing rampage early on Wednesday, officials said.
The suspected attacker, who was not identified, was in police custody, deputy emergency management coordinator for the Westmoreland County, Dan Stevens, told reporters.
Seven students between the ages of 15 and 17 and one adult were admitted to Forbes Regional Hospital in Monroeville, Pennsylvania, with stab wounds.
"These are all very serious injuries," hospital spokesman Jesse Miller said in a telephone interview.
The attacks took place in several classrooms and hallways as the school day began at Franklin Regional High School in Murrysville, 20 miles (32 km) east of Pittsburgh, county emergency management officials said. The first 911 call was received at 7:13 a.m. EDT (1113 GMT).
Three of the patients admitted were in surgery and all eight were in critical condition, hospital spokesman Miller said.
He said a ninth patient who had arrived at the hospital was airlifted to another facility.
Zak Amsler, a 17-year-old junior at the school, said the attack occurred just before his first class was scheduled to begin.
"I saw a girl with blood running out of her sleeve," Amsler said as he waited to pick up his younger sister, a student at the nearby middle school. "It was pretty mind-blowing."
Stevens, the county official, noted that the scene had been contained. "The students that are here are safe," he told reporters.
Pennsylvania Governor Tom Corbett said he had ordered state police to help local law enforcement respond to the incident.
"I was shocked and saddened upon learning of the events that occurred this morning as students arrived at Franklin Regional High School," Corbett said. "As a parent and grandparent, I can think of nothing more distressing than senseless violence against children."
The school district posted an emergency message on its website on Wednesday.
"A critical incident has occurred at the high school," the message said. "All elementary schools are canceled, the middle school and high school students are secure."
A long line of school buses was observed outside the school on Wednesday morning to take students to another elementary school nearby to be reunited with their families. (Additional reporting by Dave Warner in Philadelphia; Writing by Jonathan Allen; Editing by Scott Malone and Bernadette Baum)