The United States has formally asked Switzerland to extradite film director Roman Polanski, who fled sentencing in California on child sex charges in 1977, the Swiss justice ministry said.

Switzerland said it would make a decision on extradition based on a hearing and on information provided by Polanski's lawyer, but that there was no deadline.

"We will take the time that is needed," justice ministry spokesman Folco Galli said.

Polanski will be able to appeal against any extradition decision to the Swiss Federal Criminal Court and, in the last instance, the Federal Supreme Court, the ministry said.

The 76-year-old Oscar-winning director, who holds dual French and Polish citizenship, was arrested to comply with a US warrant when he flew into Switzerland on September 26 to receive a lifetime achievement award at a film festival.

Polanski fled the United States 32 years ago, when he was due to be sentenced for having unlawful sex with a girl aged 13.

US judicial sources have said the extradition process is complex and could take years if Polanski challenges it.

A Swiss court this week rejected a bid by Polanski for release on bail, saying the risk that he would flee was too high.

Polanski's lawyer Herve Temime told Reuters that his client's strategy remained unchanged.

"Mr. Polanski will continue to fight this extradition request and demand that he be freed," he said.

Polanski pleaded guilty to having sex with the girl in 1977, and spent 42 days in prison undergoing psychiatric tests.

But he fled the United States before the case was concluded because he believed a judge would sentence him to up to 50 years behind bars despite a plea agreement for time already served.

Polanski has avoided countries such as Britain that have extradition treaties with the United States, but he repeatedly visited Switzerland, where he owns a chalet in the mountain resort of Gstaad, though he was only arrested on this occasion.

He has never returned to Los Angeles, where his pregnant wife, actress Sharon Tate, was murdered by followers of Charles Manson in 1969.