Former Hong Kong leader Donald Tsang was sentenced to 20 months in prison on Wednesday after a high-profile corruption trial found him guilty of misconduct during his time at the helm of the city.

Tsang, 72, who held the leadership post of chief executive for seven years from 2005, is the most senior city official ever to be convicted in a criminal trial and the highest ranking one to be put behind bars.

The six-week trial at the High Court came as residents lose faith in Hong Kong's leaders after a string of corruption cases fuel suspicions over links between public officials and business figures.

Tsang was found guilty on Friday of failing to disclose his plans to lease a luxury flat from a major investor in a broadcaster, which was later granted a licence from the government while he was leader.

"Never in my judicial career have I seen a man fallen from so high," judge Andrew Chan said in delivering the sentence.

Tsang's four decades of service to Hong Kong was "indisputable", but his breach of trust was "significant", Chan told the court packed with reporters and Tsang's relatives.

He "deliberately concealed" his dealing and negotiations, the judge said.

The former leader was photographed wearing a surgical face mask, his trademark bow tie and hand restraints as he was escorted to a prison van ahead of the hearing.

He had been remanded in custody on Monday ahead of the sentencing but was hospitalised on the same night after he apparently had difficulty breathing.

- 'Dark day' -

Tsang was acquitted on another misconduct charge which alleged he had failed to declare that an architect he proposed for a government award had been employed as an interior designer on the flat.

However the jury failed to reach a verdict on a bribery charge that alleged he had taken the redecoration and refurbishment of the apartment as a kickback.

A retrial on that count was scheduled for September.

Tsang's family, including his two sons and wife, looked visibly upset as they exited the court house.

"Today is a very dark day. My family and I feel very disappointed and sad regarding today's decision by the court" his wife, Selina, arm-in-arm with her two sons, told reporters.

"We will appeal," she added.

Tsang had previously said that he had "every confidence" he would be exonerated.

But prosecutors characterised his conduct as an abuse of power to further his own personal interests.

In 2012, he apologised over separate allegations that he had accepted inappropriate gifts from business friends in the form of trips on luxury yachts and private jets.

His former deputy Rafael Hui was jailed for seven-and-a-half years in 2014 after being found guilty of taking bribes from Hong Kong property tycoon Thomas Kwok.

Hong Kong's unpopular current leader Leung Chun-ying also faces allegations of corruption over receiving a reported payment of HK$50 million ($6.5 million) from Australian engineering firm UGL before he took office.

Leung will step down as chief executive in July -- his successor will be chosen by a pro-Beijing committee representing special interest groups in March.