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 fought an uphill legal battle to persuade the coroner's court to hold an inquest, which it finally did last year.

As Coroner Monica Chow delivered the verdict on Thursday, 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.

Lawyers representing the families previously argued that government ship inspectors failed to spot a flaw on the Lamma IV -- a watertight door, shown in drawings presented during the inquest, that had not been installed.

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

Leung further criticised Chow's verdict saying: "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.

Chow ruled 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 added.

Leung called the verdict "ridiculous" and contrary to expert testimony.

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.

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

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