Hollywood actor Heath Ledger, 28, was found unresponsive Tuesday afternoon in a downtown Manhattan apartment, previously inhabited by actress Mary-Kate Olsen.

"He was found unconscious at the apartment and pronounced dead," a police spokeswoman said.

According to a New York Police Department spokesman, the Australian actor’s sudden death was possibly caused by drugs.

While no details were immediately available, NYPD spokesman Paul Browne told The Associated Press that Ledger was booked for a massage at the Manhattan apartment which is believed to be his home. He was found dead in his bed at 3:26 p.m. by his maid who went to let him know the masseuse had arrived.

"Pills were found in the vicinity of the bed," police spokesman Paul Browne was quoted by CNN as saying. "This is being looked at as a possible overdose, but that is not confirmed yet."

The medical examiner's office plans an autopsy on Wednesday, spokeswoman Ellen Borakove said.

Officials said they believed Olsen, 21, was in California and said it was not clear how long or why Ledger had been in her apartment.

Police said they did not suspect foul play in the death of the actor , who received an Oscar nomination for his role in "Brokeback Mountain" also starring Jake Gyllenhaal, about two cowboys involved in a secret relationship.

"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."

Ledger had just finished shooting "The Dark Night," a sequel to 2005's "Batman Begins," in which he will appear as the Joker. His movie credits include "A Knight's Tale," "The Patriot," and "Monster's Ball," in which he played the suicidal son of Billy Bob Thornton.

In September last year, the actor called off his engagement to Michelle Williams, whom he met while on the set of "Brokeback Mountain," although he had previously praised her as his soul mate. The two have a two-year-old daughter together, Matilda.

"Matilda is adorable, and beautifully observant and wise. Michelle and I love her so much. Becoming a father exceeds all my expectations. It's the most remarkable experience I've ever had - it's marvelous," Ledger once said.

According to the media reports, Ledger attempted suicide in September, shortly after he called off his engagement to Michelle Williams.

Meanwhile, Australians were in shock Wednesday on learning that Perth-born Heath Ledger had been found dead.

Noted film critic Margaret Pomerantz, who last met Ledger at the Venice Film Festival, where the actor was promoting the Bob Dylan biopic I'm Not There, described him as "enormously sweet but very shy" - a troubled megastar who had been awkward and had mumbled through her interview.

"It was so hard to get him to look up," she told national broadcaster ABC. "I don't think he was ever very comfortable with that press profile that is so necessary with young performers."

Ledger claimed paparazzi had driven him out of Australia when he put his Sydney harbourside house for sale in 2006. Ledger bought the house in the beachside suburb of Bronte for 4.4 million Australian dollars (3.3 million US dollars) in 2004.
"Bronte is scaring me at the moment," Ledger was quoted as saying. "I feel like the paparazzi are going to kick me out of that city."

The Australian Prime Minister Kevin Rudd said in statement: "It is tragic that we have lost one of our nation's finest actors in the prime of his life".

Neil Armfield, the Australian who directed Ledger in the local drugs-and-sex film Candy, said he was a great talent.
"He was always a complex and complicated man to work with but ... just a master, so passionately concerned to get it right," Armfield said

Nicole Kidman said his loss was "a terrible tragedy". "My heart goes out to his family," she said.