Darlene D. Lin '97 was catching up on some reading in her Leverett House dorm room. Then her pager went off, sending her to the worst disaster she's ever seen.

A seven-alarm fire charred one apartment and damaged another in the 400 block of Cardinal Medieros Drive at 6:45 p.m. last night.

Twenty-two families were displaced by the blaze, and Lin, a member of the Harvard-Radcliffe Friends of the American Red Cross, was called to offer assistance.

"I've seen buildings in bad shape, but this is definitely the biggest I've been to," said Lin, a two-year Red Cross volunteer. "Usually just one or two families are involved."

Cambridge Fire Department officials said they are unsure about the cause of the fire, which they believe began in the basement of a multi-family brick complex at 409-415 Cardinal Medieros.

Witnesses said they think at least one resident, who was thrown several yards into the air after a sudden explosion, was hospitalized.

The man was reportedly standing in the building's doorway when the blast occurred.

Cambridge Fire Department officials said two firefighters and one police officer were also hospitalized after falling on slippery pavement at the scene.

Officials would not release names of any victims.

Power outages, smoke and water damage forced residents from four apartments in a complex on adjacent Marcella Street, officials said.

Firefighters contained the blaze within 90 minutes but remained at the scene until past midnight.

"Those buildings had the power out, so they were evacuated," Lin said, noting that families without nearby relatives were transported either to a shelter or a local hotel.

Harvard Red Cross President Gerald T. Dang '97 said four undergraduates helped police and fire officials assess building damage and provide displaced families with dinner, clothes and medicine needed to get through yesterday evening.

The fire is considered the worst to strike Cambridge since February 1995, when 100 families were left homeless when a blaze ravaged Central Square.