THE father of Oscar-winning actress Nicole Kidman has died in Singapore, where police have said they are investigating his "unnatural death".

Tony Kidman, a clinic psychologist at the ­University of Technology, Sydney, was visiting the movie star's sister Antonia who lives in Singapore.

Police said they were informed a man in his 80s had died in hospital.

"Police are investigating the unnatural death," a spokesman said. He declined to give details, but the term "unnatural death" in Singapore often refers to falls or other accidents.

University vice-chancellor Professor Attila Brungs said: "It is with great sadness we learn of Dr Tony Kidman's sudden passing. During his 43 years at the University of Technology, Sydney, Tony has contributed greatly, as a colleague, as a researcher, and as a health practitioner. Our thoughts are with his family at this time."