Bialik, 36, is best known for her work on the sitcoms "Blossom" and "The Big Bang Theory."
TMZ said she was traveling alone when her white Volvo was struck in an intersection by another vehicle carrying tourists from Chile. She was taken to an undisclosed hospital where she is being treated for her injuries.
The celebrity news Web site quoted unnamed witnesses as saying there was a lot of blood at the scene.
One source told TMZ Bialik's finger was almost completely severed.
"It was just hanging there," the insider said.
TMZ did not say whether any of the people in the second vehicle were hurt or if any summonses were issued related to the collision.