Britney Spears was rushed to a Los Angeles hospital over night after police were called to her Studio City home.

At around 8 p.m. police responded to a call “about a custodial dispute regarding Britney Spears’s children,” said LAPD officer Jason Lee.

Nearly three hours later, police determined that a court order stated that the singer’s children, who were with Spears at the time, were supposed to be with Kevin Federline, and a transfer was arranged, according to Lee.

“While officers were on the scene, they observed Ms. Spears under the influence of an unknown substance,” Lee added. “She is now being taken in for an evaluation, more than likely to a hospital. There were no reported injuries to anyone involved including the children.”

In addition to multiple officers, fire trucks, two ambulance and a police helicopter were all on the scene. At one point, Spears was seen being taken to an ambulance on a gurney.

After Spears arrived at the hospital, her father, Jamie, and her ex, Federline – as well as both of her sons – were spotted there. A source confirms that the boys were not being treated for any injuries.

Spears, who has visitation rights with her two sons Preston, 2, and Jayden, 1, was scheduled to give the boys over to Federline at 7 p.m. Thursday. A bodyguard for Federline arrived to pick up the boys at the designated time, but Spears refused to relinquish her sons, according to a source.

Police – as well as Federline’s lawyer Mark Vincent Kaplan – arrived at the house close to 8 p.m., though Kaplan was later seen leaving.

Earlier in the day, Spears showed up 90 minutes late to a scheduled deposition in her custody case – and stayed for only a fraction of an hour.

Back at her Studio City home directly after the hearing, when a photographer asked if Kaplan was nice to her, Spears, 26, responded with an emphatic, “No!”

When reached, Spears’s lawyer Sorrell Trope, who on Wednesday filed a request to withdraw from the singer’s custody case, said only: “No comment.”