BOSTON -- An out-of-control delivery truck carrying medical supplies apparently triggered a chain reaction of multiple car crashes in Boston's Allston neighborhood early Thursday, sending at least three people to the hospital and snarling the busy morning commute.

Two motorists were taken to Brigham & Women's Hospital and the truck driver was sent to St. Elizabeth's Hospital, authorities said. Their conditions were not released, but none of the injuries were thought to be serious.

"We have one car sitting on a sidewalk into a pole. We have another car that's into a building. Apparently, this truck was coming up Commonwealth Avenue going westbound, hit several cars. Fortunately, we only have three injuries including the truck driver. Right now we're trying to determine what happened. It's really a chaotic scene," Boston Fire Chief Steve McDonald said.

Early reports were that the initial crash at about 7:20 a.m. involved a New England Delivery box truck carrying medical supplies. It crashed into a car near Commonwealth Avenue and Babcock Streets, hit several other parked vehicles, and then finally stopped near Brighton Avenue, where it burst into flames.

"At scene number one, a white truck struck five cars. Continued down Commonwealth Ave., striking three more vehicles at Brighton and Comm. All in all, nine cars involved in the accident," Boston Police officer James Kenneally said.

The truck's contents, headed to Franciscan Children's Hospital, were highly flammable, so it was treated as a Level 3 hazardous materials scene. Several buildings were evacuated while the accident was cleared, fire officials said. Litter and debris remained all along Commonwealth Avenue by midday, but police said the contents of the truck were eventually determined not to be dangerous.

"He told me that he really didn't remember what happened, that he thinks he blacked out and he remembers hitting the gas pedal instead of the brake," said a friend of the truck driver who identified herself only as Tina.

The first cars hit were at Babcock Street, but the truck kept moving for several blocks, totaling a white parked car in its path and then hitting a Range Rover, which it sent crashing into a nearby storefront at Packard's Corner, where Brighton Avenue and Commonwealth Avenues intersect, police said.

"We were coming to get our car before work and we saw all the yellow tape and noticed that it was our car and that all my stuff was in the street," said Janell Ridenour said.

Both crash scenes are within a few blocks of Boston University's Nickerson Field.

Commonwealth Avenue outbound was closed to traffic. In one of the crashes, a pickup truck came to rest on the Green Line MBTA tracks, causing T officials to suspend Green Line service between Packard's Corner and Kenmore Square until about 10:30 a.m., creating major hassles for morning commuters along the busy route that serves several area universities.

"All the colleges, BC out, BU inbound, people going to work, the Kenmore Square area, the Back Bay area, so (the impact is) significant," a Boston patrolman said.

Welders had to cut through MBTA metal fencing to free the truck that was sent careening into nearby track area.

"I'm headed to work in Kenmore Square. I can't believe that. It's just the saddest thing I've ever seen," one commuter said.

Motorists were advised to seek alternate routes and many commuters had to walk for blocks to catch an MBTA bus.

"Yeah, I'm going to be late for class. I don't know how late, hopefully not that late, but Northeastern (University) is still a little ways away," student Dave Church said.

The good news, MBTA officials said, was that the Green Line was expected to be back to normal for the afternoon commute.