Charlie Sheen was rushed to the hospital this morning, TMZ has learned ... and a source at the hospital tells us, "It's serious."

We're told Charlie was taken out of his home on a stretcher and loaded into an ambulance at 7 AM.

Two young women exited the house at the same time Charlie was taken out with a towel partially over his face.

Charlie was transported to Cedars-Sinai Hospital in L.A. We're told tests were performed and doctors are waiting for results.

The 911 call was placed at 6:35 AM.

Sources say Charlie was having severe abdominal pains which triggered the 911 call. Stan Rosenfield, Charlie's publicist, tells TMZ Charlie was in the emergency room this morning -- sleeping.

We're told Charlie's father, Martin Sheen, and his mom, Janet Templeton, are at the hospital. Charlie's ex-wife, Denise Richards, is also there.

UPDATE: Neighbors tell TMZ Charlie threw some sort of party last night. They heard women inside Charlie's house singing Red Hot Chili Peppers songs throughout the evening. The party went on -- loudly -- well into the wee hours.