Switzerland's top criminal court on Tuesday rejected Oscar-winning director Roman Polanski's request to be released on bail, saying there was a "high" risk that he could flee the country.

"The Swiss Federal Criminal Court has rejected Roman Polanski's appeal against detention pending extradition," the court said in a statement.

"The court considered the risk that Roman Polanski might flee if released from custody as high," it added.

Polanski has been regarded as a fugitive by US authorities since he fled the United States in 1978 after admitting to sex with a 13-year-old girl.

He was detained by Swiss police acting on an extradition warrant when he went to Zurich to collect an award at the city's film festival.

"According to Swiss law, detention is the rule during the entire extradition proceedings," said the court.

Polanski had put up his chalet in the glitzy Swiss ski resort of Gstaad as bail, according to court documents.

However, Switzerland's federal criminal court assessed that the bail was not in line with requirements set by the law.

Highlighting the high risk of flight, the court noted Polanski's dual French and Polish nationalities, and pointed out that he could travel across the borderless Schengen zone "without problem and without travel documents."

He could also leave the country using a private plane or helicopter, said the court.

Appeal would be lodged

"In view of the circumstances, that the appellant can practically leave the country in a matter of hours from any point in Switzerland and in particular to escape to France, even a requirement for him to report daily to the police would be unable to effectively prevent an escape," it said in its ruling.

Polanski's French lawyer said an appeal would be lodged with the Swiss supreme court.

"I take note of the decision. We will file an appeal before the Lausanne tribunal," said lawyer Herve Temime.

"We will try to provide even stronger and more suitable guarantees," Temime said. "We will seek to demonstrate that there is no risk in ordering Roman Polanski's release."

The decision by the criminal court was in line with the Swiss justice ministry's decision on October 6 to oppose bail for the 76-year-old film-maker.

Swiss justice ministry spokesman Folco Galli said then that authorities felt there was a "great danger" that Polanski would flee the country pending a full extradition request from the United States on the three-decades-old case against him.

Under an extradition treaty with the United States, prosecutors in California have 40 days from the time of Polanski's arrest to lodge their full extradition request, which the court will subsequently rule on as well.

Polanski was admitted to hospital over the weekend for medical tests, and was due to be returned to prison.