SAN FRANCICSO -- A woman died after she was fatally struck by a San Francisco Municipal Transit Agency bus while crossing a Tenderloin street early Tuesday.

The No. 27 Bryant bus was making a right turn from Ellis Street onto northbound Leavenworth Street when it struck the woman as she crossed westbound on Leavenworth, San Francisco police Sgt. Kevin Phipps said.

It wasn't clear if the woman had a green light or if she was in a crosswalk, Phipps said. Her body, covered with a yellow tarp, was lying several feet away from the crosswalk as police and the medical examiner investigated the 7:33 a.m. accident.

Phipps identified the woman only as an Asian adult.

A motorist who identified himself as Tim said he saw the accident while parking his car on Leavenworth Street.

A small woman was running across the street when she was hit and thrown under the wheels of the bus, he said.

Linda Moore said she was walking to work down Leavenworth Street when she came upon the crash seconds after it happened. She and a fellow pedestrian, who happened to be a licensed vocational nurse, ran to help the victim.

The nurse felt for a pulse, but the woman was already dead, Moore said.

"We just covered her up. She was wearing a hooded sweater, and we put the hood over her head. There were tire marks on her clothes," Moore said.

The victim looked "no more than 18," Moore said.

Several passengers appeared to be on the bus when it struck the woman, Moore said.

Paramedics responded to the accident and pronounced the victim dead.

Muni spokesman Alan Siegel said the accident was a police investigation and that Muni had no comment.

This is the second Muni-related pedestrian death in just over two weeks. On March 18, Edwardo Funes was killed on a J-Church track near Dolores Park. Police determined that death was a suicide.