SEPTA investigators are looking at both human error and mechanical malfunction as a possible cause for the collision between two rush-hour Regional Rail trains in a tunnel under Center City, an agency spokesman said yesterday.

A total of 32 people were injured in the incident about 5 p.m. Monday, eight of them SEPTA employees, said spokesman Gary Fairfax. None of the injuries was life-threatening.

Between 900 and 1,100 people were on the two trains when the R6 to Norristown was rear-ended by an R5 to Doylestown outside the Market East Station, Fairfax said.

The R5 was traveling about 5 m.p.h. at the time, comparable to the speed used when train cars are coupled, he said.

The R5 backed up to Market East and the R6 traveled to the Temple University station, where a fleet of ambulances was waiting for the injured.

The injured were treated at Temple, Hahnemann and Jefferson University Hospitals, Fairfax said.

Some passengers complained about the lack of communications from SEPTA crews on the trains after the collision.

Brian Matthews, 39, of Philadelphia, said no announcements were made on the R6.

"That's a situation ripe for panic," he said.

Contact staff writer Joseph Gambardello at 215-854-2153 or jgambardello@phillynews.com.