Scores of people are feared to have drowned after a passenger ferry capsized off the coast of Guyana on Saturday night local time.

Sixty-seven people were rescued on Sunday, officials said, but since then rescue workers have been unable to locate any more survivors.

According to the ferry's passenger list, it was carrying 116 passengers and 17 crew, but Guyana's prime minister has warned that the list is not accurate.

Divers continue to search the site where the vessel capsized and people who believe their loved ones may have been on board the stricken vessel have been asked to contact the authorities.

Prime Minister Mark Phillips said an investigation had been launched into the ferry's loss.

"Let me be absolutely clear: where negligence, misconduct or criminal wrongdoing is established, those responsible will face the full force of the law," he said.

Guyana's Public Works Minister, Juan Edghill, expressed his anger at a news conference on Sunday, accusing those who operated the ferry of trying to "cheat the system".

He said that out of the 67 people rescued, only 35 had been listed on the passenger manifesto, leading to fears that there may have been dozens more people on board than the 133 on the official registry.

Edghill also said that the ferry's captain and at least one crew member had tested positive for cannabis.

"We have zero tolerance for members of the crew drinking or smoking while at work. And for us to have positive tests from the captain... this is serious," the minister said.

He added that the captain and several of his crew had been taken into police custody.

Search teams located some of the life crafts, but some survivors reported clinging on to boxes

The ferry, MV Barima, departed from the capital, Georgetown, on Saturday afternoon local time, headed for Port Kaituma, in the north of the country.

The 40m-long (131ft) vessel was built in 1939, according to a listing on VesselFinder.

A survivor, Elena Moonsammy, told local news site Kiskadee Watch that the ferry had tilted after being hit by a large wave, with water quickly rushing in.

It started to take on water within seconds, she said.

A distress call was received at 23:01 (03:01 GMT Sunday), triggering a search operation involving government teams and privately owned boats.

Moonsammy said she had survived by clinging to a box floating amidst the debris.

She had tried to hold on to the hand of her two-year-old child but they had been separated.

Moonsammy said she had managed to save a woman, whom she urged to also hold on to the floating box.

Among the 67 people rescued are 15 children. Small private boats were key in pulling at least 17 survivors from the sea.

Guyana's Health Minister, Dr Frank Anthony, said three of the survivors remained in hospital with minor injuries but the others had already been discharged.

Most, he added, had cuts and bruises from clinging to debris for hours.