Demi Lovato rushed to hospital following medical emergency at her Hollywood Hills home

HOLLYWOOD HILLS, LOS ANGELES -- Demi Lovato was rushed to a hospital following a medical emergency at her home in the Hollywood Hills Tuesday afternoon, sources tell ABC News.

The Los Angeles Fire Department received a medical call from a home along Laurel View Drive in Hollywood Hills on Tuesday shortly before 11:30 a.m.

Fire officials confirmed that a 25-year-old woman was transported to a local hospital. Police and fire officials have yet to confirm the identity of that woman.

But multiple sources told ABC News that Lovato is being treated at Cedars-Sinai Medical Center. Her condition was unknown.

Lovato has been outspoken about her battles with bipolar disorder and substance abuse.

In March, the singer retweeted a post of an interview she gave, during which she said she was six years sober.

In May, she tweeted that new music and lyrics would reveal the truth.

Just last month, Lovato released a new song called "Sober," which includes lyrics indicating she was not sober anymore.

According to Lovato's website, upcoming tour dates have been rescheduled.

Fellow musicians and celebrities, including Ariana Grande, Brad Paisley and Ellen DeGeneres have been reacting to the news on Twitter: