Ex-Nissan chief Carlos Ghosn leaves Japan prison on bail. (File)

Former Nissan chief Carlos Ghosn left a Tokyo jail on Wednesday after more than 100 days of detention, a day after a surprise court decision granting him bail of one billion yen ($9 million).

Ghosn left the detention centre in northern Tokyo flanked by prison guards, wearing a blue cap, a white medical face mask and a work jacket with orange reflective stripes.

His bail was the latest twist in a case that has gripped Japan and the business world since the auto industry titan's November 19 arrest.

The 64-year-old faces three charges of financial misconduct over allegations he under-reported his compensation and tried to shift losses to Nissan's books.

He has strongly denied the claims, and said in a statement overnight he was looking forward to his day in court.

"I am innocent and totally committed to vigorously defending myself in a fair trial against these meritless and unsubstantiated accusations," he said.

Prosecutors could still seek to rearrest Ghosn if they file new allegations against him, but for now the auto tycoon is out of detention thought still facing strict limits on his movement and communications.

Ghosn had applied for bail twice previously without success, but he shook up his legal team last month, hiring renowned defence attorney Junichiro Hironaka, who quickly filed a new request.

The court had previously justified Ghosn's ongoing detention by saying he posed a flight risk and could seek to destroy evidence, so Hironaka's bail request offered restrictions intended to win the court's trust.

New restrictions

The bail terms prevent Ghosn from leaving Japan and include other measures restricting his communications.

Kyodo news agency said the measures will restrict Ghosn's cell phone use and allow him to access a computer only in his lawyer's office during daytime hours on weekdays.

He will also be banned from contacting Nissan executives and other people with links to the allegations against him, the agency reported.

But Kyodo said Ghosn could still attend board meetings at Nissan, where he remains a director, if the court gives approval.

Ghosn's prolonged stay behind bars had come under fire internationally and from rights groups.

Speaking to AFP and French daily Les Echos in January -- his only interview with foreign media so far -- Ghosn himself said that his continued detention "would not be normal in any other democracy".

"Why am I being punished before being found guilty?" Ghosn asked.

Under Japanese law, prosecutors can hold a suspect for up to 22 days while they investigate an allegation, and then can apply for repeated one-month stretches of pre-trial detention for each charge eventually levelled.

That means prosecutors could force Ghosen to return to jail if they level new allegations against him, restarting the 22-day detention clock.

'The Razor'

In a shake-up of his legal team last month, Ghosn replaced a former prosecutor known as "The Breaker" with Hironaka, who has earned the nickname "The Acquitter" for his court record and "The Razor" for his mental sharpness.

Speaking to reporters on Monday, Hironaka had vowed a "completely new legal strategy" to obtain his client's release, and experts said the change of tack appeared to be behind the surprise bail ruling.

"I think the content of the lawyer's application changed the situation," said Japanese lawyer Nobuo Gohara.

Nissan declined to comment on the bail decision, saying it was a matter for courts and prosecutors.

However, it said that an internal probe had "uncovered substantial evidence of blatantly unethical conduct" and that "further discoveries related to Ghosn's misconduct continue to emerge".

"The company's focus is firmly on addressing weaknesses in governance that failed to prevent this misconduct," it added in a statement.

A towering figure once revered in Japan for turning around Nissan's fortunes, Ghosn also forged a successful alliance between Nissan, Mitsubishi Motors and France's Renault.

But his attempts to deepen the alliance caused resentment in some quarters, and Ghosn has claimed the allegations against him are part of a "plot" by opponents of greater integration between the three firms.

Given the number of people involved in the complex case and their wide geographical spread, Hironaka said the case would run over a "very long time span".

However, he said prosecutors had begun handing over some of their evidence prior to a potential trial.