NEW YORK (CNN) -- Actor Heath Ledger was found dead Tuesday of a possible drug overdose in a Lower Manhattan apartment, the New York Police Department said.

Heath Ledger was unresponsive when a housekeeper found him in a Manhattan apartment Tuesday. more photos »

The Academy Award-nominated actor was 28.

Ledger was found naked and unresponsive, facedown on the floor at the foot of his bed by a housekeeper trying to wake him for an appointment with a masseuse, said police spokesman Paul Browne.

"Pills were found in the vicinity of the bed," he told CNN.

"This is being looked at as a possible overdose, but that is not confirmed yet."

Browne later told reporters some prescription medications were found in the room, including sleeping pills.

But he stressed police have made no determination of the cause of Ledger's death -- that would be done by the medical examiner.

He said the pills were not "scattered about."

No note was found and there was no indication of foul play, Browne said. Ledger was found at about 3 p.m., and was pronounced dead at the scene by emergency personnel about 3:30 p.m. Watch a report about Ledger's death »

A crowd of onlookers, photographers and reporters gathered outside the apartment building after news of Ledger's death was reported. Police officers were guarding the doors.

Browne said he did not know how long Ledger had been renting the apartment, which he said took up the entire fourth floor.

An autopsy would be conducted on Wednesday, said Ellen Borakove, spokeswoman for the New York City medical examiner's office. Watch Ledger's body being removed »

Ledger's family called his death "very tragic, untimely and accidental."

"Heath has touched so many people on so many different levels during his short life, but few had the pleasure of truly knowing him," his father said.

"He was a down-to-earth, generous, kindhearted, life-loving, unselfish individual extremely inspirational to many."

Hollywood reacts

Condolences began pouring in from Ledger's friends and co-stars.

"I had such great hope for him," said Mel Gibson, who played Ledger's father in "The Patriot," in a statement.

"He was just taking off and to lose his life at such a young age is a tragic loss. My thoughts and prayers are with him and his family."

Actress Nicole Kidman, a fellow Australian and close friend of Ledger's, said in a statement, "What a tragedy. My heart goes out to his family." Watch the reaction at the Sundance Film Festival »

At the time of his death, Ledger had just finished playing the villain The Joker in "The Dark Knight," the latest installment in the Batman series. The film is to open in July.

Ledger was born in Perth, Australia, and named Heathcliff Andrew after the main characters of Emily Bronte's "Wuthering Heights." He began acting at a local theater as a child. Find out more about the actor »

Ledger's first American film was the teen comedy "10 Things I Hate About You" in 1999, and he immediately attracted attention from Hollywood. He passed up several scripts before taking a role in the Revolutionary War drama "The Patriot" in 2000 and "A Knight's Tale" in 2001. He also played a supporting role in "Monster's Ball," among other films. See a photo gallery of Ledger's life and career »

"In a way I was spoon-fed a career," he told the Glasgow Herald in 2005. "It was fully manufactured by a studio that believed it could put me on their posters and turn me into a product. ... I hadn't figured out properly how to act, and all of a sudden I was being thrown into these lead roles."

Controversial role

But Ledger was perhaps best known for his 2005 portrayal of Ennis Del Mar in "Brokeback Mountain," about two cowboys who had a secret romantic relationship. The role earned him an Oscar nomination.

"I felt that choices were being made for me, so I feel this has been my time now to find the good stories and test myself," Ledger told the Glasgow Herald in the 2005 interview. "It has been an interesting year, where I finally have a sense of accomplishment."

Asked how he felt about filming love scenes with another man, Ledger said he and his co-star Jake Gyllenhaal simply focused on their roles.

"We can't say that we weren't nervous about it," Ledger told Oprah Winfrey in 2006. "But once the first take was over, it's like, 'OK. So what? It's kissing another human being. How are we going to finish this scene? Let's get on with it and let's get out of here.' "

In a written statement, the Gay and Lesbian Alliance Against Defamation said it mourns Ledger's death, adding that his portrayal of Del Mar "changed hearts and minds in immeasurable ways."

Ledger has a daughter, Matilda Rose, born in 2005 to his then-girlfriend, Michelle Williams, who played his on-screen wife, Alma, in "Brokeback Mountain." The couple have since separated.

"He was just so respected in the industry," said Kim Serafin, senior editor of In Touch Weekly.

"It's just horribly tragic. He was just a fine actor and a good person, so this is horribly sad and very unexpected." E-mail to a friend

CNN's Deb Feyerick, Susan Chun, Miguel Susana and Eden Pontz contributed to this story.

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