Tanzania’s president John Magufuli has ordered the arrest of the managers of a ferry that capsized in Lake Victoria, after the death toll climbed above 130 and rescue workers pressed on with the search for scores more still missing.

Initial estimates suggested that the MV Nyerere was carrying as many as 300 people when it capsized near the dock on the island Ukara. The precise number was unknown, however, because the ticket-seller had drowned and the machine recording sales had not been found.

During a speech on public television on Friday night, Magufuli referred to “negligence” and said he had ordered the arrest of “all those involved in the management of the ferry”.

Facebook Twitter Pinterest Tanzania’s president John Magufuli Photograph: Reuters

“It appears clear that the ferry was overloaded,” he said, adding that “the arrests have already begun”.

The president also declared four days of national mourning, while saying at least 131 people had died, updating an earlier death toll of 126.

At least 40 people were brought to safety on Thursday, some in “a very bad condition”, said John Mongella, the commissioner for the Mwanza region in northern Tanzania.

It was unclear whether any new survivors have been found since rescue operations resumed on Friday morning, and hopes were fading that more survivors might still be found.

Dozens of security forces and volunteers wearing gloves and face masks spent the day hauling bodies into wooden boats.

Tanzanian ferries often carry hundreds of passengers and are overcrowded, and there are shifts in weight as passengers move to disembark. The Nyerere was crowded because it was a market day.

Domina Maua, who was among those at the dockside seeking information about survivors, said: “I have not heard from either my father or my younger brother who were on the ferry. They had gone to the market in Bugolora to buy a school uniform and other supplies for the new school term.”

Facebook Twitter Pinterest Rescuers search for bodies off the shores of Ukerewe Island on Lake Victoria. Photograph: Reuters

Davita Ngenda, an elderly woman in Ukara, wept as she said. “My son is among the bodies recovered. He had gone with his wife but she has not been found yet. My God, what did I do to deserve this?”

Sebastian John, a teacher, said such tragedies were part of life for those who lived near the lake. “Since my birth, people have gone to their deaths on this lake, but what are we to do? We did not choose to be born here, we have nowhere to go,” he said.

The ageing ferry, of which the hull and propellers were all that remained visible, was also carrying cargo, including sacks of maize, bananas and cement, when it capsized about 50 metres from Ukara dock. The cause of the accident was not immediately clear, but overloading is frequently to blame for such incidents.

The country’s opposition, however, accused the government of negligence. “We have often raised concerns about the poor condition of this ferry, but the government turned a deaf ear. We have repeatedly denounced this negligence,” said John Mnyika, the deputy secretary-general of Chadema, the main opposition party.

Mnyika said overloading was “another failure of the authorities” and criticised “inadequate relief efforts as well as delays” in the rescue operation.

With a surface area of 70,000 sq km (27,000 sq miles), the oval-shaped Lake Victoria is shared by Tanzania, Uganda and Kenya. Capsizes are not uncommon and the number of deaths is often high because of a shortage of lifejackets and the fact that many people in the region cannot swim.

Play Video 0:49 People on the capsized hull of sunken ferry in Tanzania's Victoria Lake – video

The deadliest such incident in recent decades was in May 1996, when about 800 people died after their ferry sank on the way to Mwanza in Tanzania.

Lake Victoria’s waters can be rough and boats are frequently poorly maintained, while ferry operators often fail to record the number of passengers on board.

About 20 people were killed in December 2016 when a boat overturned on the lake as it was carrying passengers to mainland Uganda for the Christmas holidays. In March 2012, only two survivors were found after a boat carrying about 60 people capsized on the lake in Uganda.