The father of actress Nicole Kidman died in Singapore on Friday, a source told AFP, with Australian media saying he had fallen while visiting the Oscar winner's sister.

The source, who is familiar with the case, said Antony Kidman passed away after he was brought to a state-run hospital.

Singapore police said an elderly man had died at the hospital on Friday but did not give his name.

"Police were informed today at about 9.45am that a man in his 80s was pronounced dead at Tan Tock Seng Hospital," a Singapore police spokesman said.

"Police are investigating the unnatural death," he added.

The spokesman did not comment on the circumstances of the death but Australian media said he had suffered from a "fall".

The Sydney Morning Herald said Antony Kidman was visiting Nicole's sister Antonia, who lives in Singapore.

It said he was a clinical psychologist and director of the health psychology unit at Sydney's Royal North Shore Hospital.

News Corp-owned news.com.au said the senior Kidman "had a very close relationship with his daughters Antonia and Nicole and their families".

The family was last seen together in Sydney in January for the 50th wedding anniversary of the senior Kidman and his wife Janelle, the website said.

Nicole Kidman, 47, most recently starred in Grace of Monaco, a biopic of the American film actress and Princess of Monaco.

Kidman won an Academy Award for her portrayal of author Virginia Woolf in The Hours in 2002.

Expressions of sympathy were posted on the star's Facebook page although she has yet to issue a statement.

"My dear sweet Nicole I just heard that your father passed away. I am so very sorry and I am in tears," one of the postings read.

Another post said: "Our thoughts and prayers are with and your family at this sad time."