The accident happened just before 3 p.m.
At least 47 people were treated for injuries. Muni reported four people in critical condition including a Muni operator. It took three hospitals to handle the emergency but the most serious victims were taken to San Francisco General Hospital where administrators issued a level-1 alert to let staff know there was an emergency.
By Saturday evening, most patients seemed to be okay and some had even gone home.
As 16-year-old Jonathan Wei limped out of the hospital Saturday night he described to ABC7 the chaotic scene on board San Francisco's L train as it crashed.
"People were screaming in Chinese, "It hurt so much. It hurt so much." And, people were hella shocked, like what happened?" he said.
Their L-Taraval train slammed into a K-Ingleside train at the West Portal station just before 3 p.m. Passengers say the L was moving pretty fast. The K was standing still.
"I saw people flying and stuff. I hit my head on the transfer thing right there," said Wei.
48 people were hurt, four of them severely.
"None of the injuries in today's collision were described as life-threatening by the fire department at the scene. That could change, but the initial indication was no-life threatening injuries," explained Muni spokesman Judson True.
There were so many victims to tend to that some ambulances carried more than one person. A Muni bus even had to drop off some of the walking wounded at the hospital where concerned loved ones packed into the waiting room trying to get some information. Many of them had talked to the victims on the phone, but had only received part of the story.
"She said three people almost died! Died?" said Son Li, one passenger's nephew.
No one died in the crash, but passengers said listening to the screaming on board and seeing the blood was pretty scary.
"Some of them were acting kind of crazy. Others were calm," Wei said.
Witnesses say the L train did not look like it was slowing down at all as it approached the platform and the driver appeared slumped over.
"I saw this barreling in, not slowing down. The driver's head was down. He looked like he was asleep or passed out. I couldn't tell. But he was not looking at me," witness Nancy Martin told ABC7.
Investigators say they do not know how fast the train was going or what, if anything, happened to the driver before the crash. He was one of the four seriously injured.
"We take this accident incredibly seriously. We'll do everything we can to investigate what caused it as expeditiously and thoroughly as possible because we know it's unacceptable, and we want to do everything we can to make sure it doesn't happen again," said True.
Jonathan Wei has a separated shoulder, a banged-up knee, and a knot on his head. But, he is not complaining.
"I feel okay right now. I think I'm kind of lucky because other people got really injured," he said.
Investigators said Saturday it should not take that long to figure out how fast that train was going.