The Lamma IV ferry sank after colliding with another vessel on October 1, 2012, killing 31 adults and eight children in what became the Chinese city's deadliest maritime disaster since 1971.

Victim representatives partly blame the tragedy on shipbuilders who did not follow design drawings to install a watertight bulkhead door, and on government inspectors who failed to spot the omission.

But coroner Monica Chow concluded that the ship would have sunk after the collision even if the door had been attached.

The door's absence "did not constitute a design error nor amount to a breach of the regulatory requirements in force at the time", she said as she delivered the verdict.

Chow added on Thursday that the families were demanding "near-perfect scrutiny" from overworked inspectors, which was "impractical" and "unrealistic".

As Chow spoke, about half a dozen family members stormed from the courtroom, local media reported.

"I can speak on behalf of all the family members... we are extremely disappointed," sales manager Alice Leung, who lost her brother in the incident, told reporters at the West Kowloon law courts building.

"For 13 years, we wanted to find the truth about who was responsible, and what we got was the word 'unrealistic'. I'm outraged."

Ryan Tsui, whose brother and niece were killed in the tragedy, said the verdict wasn't just for grieving families but should have addressed society's concerns.

A prior investigation found that the missing door contributed to the ferry's rapid sinking, which gave passengers little hope of escape.

The inquest spanned more than 40 days and involved 84 witnesses, including shipyard directors, inspectors and mariners.

The coroner has no authority to hand down punishments, but directed her criticism towards a senior government ship surveyor who gave inconsistent evidence.

Hong Kong courts jailed the two captains involved in the crash in 2015, and a year later, two government employees who failed to ensure lifejacket compliance.

A government spokesman said late Thursday that it would "study the verdict carefully with serious follow-up" and expressed condolences to the families.

The government had taken disciplinary action against some Marine Department officers following an internal probe, the spokesman said, without naming the people.

Leung said she was hoping to stop her 13-year search for accountability, but she felt there was no end in sight.

"I believe that the families will not give up," she said.