A Hong Kong boat captain has been sentenced to eight years in prison for the manslaughter of 39 people in a 2012 ferry collision, the city's worst maritime disaster in nearly four decades.

Sea Smooth skipper Lai Sai Ming, 56, was found guilty on Saturday following a trial that gripped the city, over the accident between his high-speed ferry and a pleasure boat near Lamma Island.

"I have concluded you should go to prison for eight years," judge Brian Keith said on Monday.

"It's been a personal tragedy for you and your family but it cannot begin to compare with the grief of those who lost their loved ones," he said, as Lai listened from the dock with his head lowered.

Lai was jailed for a further 18 months for endangering the safety of others at sea, but the terms will be served concurrently.

Chow Chi-wai, 58, who was steering the leisure boat Lamma IV with 120 people on board during the collision on October 1, 2012, was jailed for nine months for endangering others' safety at sea. He was acquitted of all 39 charges of manslaughter.

Saturday's verdict came after a nine-member jury deliberated for four days following a 60-day trial.

The collision raised questions over safety in the crowded waters of Hong Kong, one of the world's busiest ports, with an inquiry pointing to a "litany of errors" that caused the disaster.

It was the city's most serious maritime accident since 1971 when a ferry between Hong Kong and Macau sank off the island of Lantau during a typhoon, killing 88 people.

Source: AFP