SAN FRANCISCO (AP) — A streetcar and bus collided Wednesday in downtown San Francisco, sending at least 15 people, including seven children, to a hospital, authorities said. None of the injuries were serious.

The people were among dozens of riders injured as the trolley rear-ended the bus at a stop along the city's busy Market Street thoroughfare shortly after 11 a.m., said Paul Rose, a spokesman for the San Francisco Municipal Transportation system.

A number of people were treated at the scene, with bumps and bruises being the most significant injuries, said Mindy Talmadge, a San Francisco fire department spokeswoman.

The injured children were aboard the bus when it was struck, Talmadge said.

"Luckily, there were no serious injuries," she said.

The driver of one of the vehicles was among those taken to the hospital, Rose said. Both vehicle operators will be given drug and alcohol tests and placed on non-driving status, Rose added.

The cause of the collision and speed of the trolley were under investigation, said Ed Reiskin of the San Francisco Municipal Transportation agency. Surveillance videos onboard both vehicles will be included in the probe, he said.

"We'll pull everything apart," Reiskin said. "Anytime we have any kind of incident, it's something we take very seriously. Our mission is to move people safely through the city."

The injured children were part of a day camp group heading to the Cable Car Museum. Several could be seen sitting on the sidewalk holding ice packs to their heads after the collision.

Another city bus eventually arrived and took about two dozen kids — several smiling as they boarded — to the Cable Car Museum.

Both vehicles involved in the collision were towed from the scene, with service resuming about 12:45 p.m.

In February, seven people were injured in a cable car that came to a sudden stop after striking a 1.5 inch bolt stuck in tracks in the city's Nob Hill neighborhood.

Officials said the bolt did not belong to the cable car. A conductor underwent surgery after suffering facial and tongue injuries, and a gripman suffered internal injuries and cracked ribs.