Sources connected to Kate tell TMZ ... the 'Underworld' star has been staying at The Signature at MGM Grand while in town to shoot the film, "Prisoner's Daughter." We're told around 10:30 AM Friday morning, her back went out and it was bad enough that she was rushed to a nearby hospital by ambulance.
We're told at the time of this posting Kate is still in the ER. Her condition is unclear ... we're told this is all happening in real-time.
Kate posted a photo on social media Thursday from Vegas ... we're told she's been there about a week shooting the movie.
Beckinsale became a Hollywood starlet in the late '90s after starring in "Brokedown Palace," but really broke out the next couple years with roles in "Pearl Harbor" and "Serendipity."