Police were investigating a crash involving a cement truck that killed a woman on a bicycle in front of AT&T Park in San Francisco Saturday morning.

Officers responded to reports of the collision near the intersection of Third and King streets around 9:37 a.m., police said.

Both the woman and the cement truck were heading westbound on King St when, for unknown reasons, they collided, Sgt. Michael Andraychak said.

The driver stopped immediately after the crash and was cooperating with the police investigation, he said.

The woman was taken to a hospital with life-threatening injuries and was pronounced dead later that morning.

The medical examiner's office identified the victim as 48-year old San Francisco resident Diane Sullivan.

Investigators were attempting to determine how the crash happened and police said the cement truck driver is cooperating with investigator.

“You do have a big cement truck with a big wheel base and preliminary reports are that she was curbside on her bike, riding, and somehow became entangled,” said San Francisco police Sgt. Frank Harre

Alcohol and drugs do not appear to have been a factor, police said.

The fatal collision occurred as thousands of people waited to enter the San Francisco Giants Fan Fest.

Police said two nurses who were in the crowd heading to the park stopped to help Sullivan.

The incident left many in shock.

 “I've never seen someone trying to get someone else breathing again actually in person, so that was unfortunate,” said Amber Gregory of San Francisco. “I feel terrible.”