Survivors of a ferry accident off the popular tourist archipelago of Zanzibar in which at least 193 died on Saturday, according to a minister, said overcrowding caused the disaster.
Rescue workers managed to save 612 people from the MV Spice Islander until being forced to suspend their work as night fell, Zanzibar's state minister for emergencies Mohammed Aboud said.
The ferry, travelling between Unguja and Pemba -- two of the three islands that make up Zanzibar -- left Unguja around 9:00 pm on Friday (1800 GMT) and capsized four hours later.
Some angry survivors accused port and ferry officials of having ignored the protests of passengers and overloaded the boat.
State emergencies minister Aboud told AFP Zanzibar had "asked for emergency assistance from Dar es Salaam, including divers to help in the rescue efforts."
The ferry was reportedly carrying a heavy cargo of rice and other goods.
"Rescue operations are being hampered by a lack of equipment," deputy secretary of state for infrastructure and communication Issa Gavu told AFP.
Rescue diver Ali Shante who arrived at scene some five hours after the ferry capsized said many of those rescued were "found floating using mattresses, wood and bags of rice."
Some survivors who arrived back in Stone Town, the main port of the archipelago, where an emergency first aid centre was set up to treat those brought to land by rescue speed boat, described their ordeal.
"It was terrifying, people were screaming and shouting in the dark," recounted seven-year-old Aisha Mohammed.
"I can't find my mummy, I lost her when we were all in the water," she added after being picked up by a rescue boat.
Others blamed the operators and port officials for having caused the accident.
"We were shouting at the captain and at the people in the port even before we left that the boat was too full -- it was packed with people and with cargo," said Zaid Amour, 50.
"This was not an accident but is the fault of those who did not stop the boat from leaving when it was clear to passengers it was not safe."
"Sailors on the boat were still telling us 'it is ok' when we were calling for life jackets, so when things got really bad it was too late for many people," Amour added.
The government pledged to do all it could to help.
"This is a national tragedy, so let us join hands together over this," Zanzibar's President Ali Mohamed Shein said, before announcing that the archipelago would observe three days of national mourning from Sunday.
"The government of Zanzibar will do everything that it can to support the victims of this terrible event," he added.
Tanzania's President Jakaya Kikwete described the event as "a big tragedy to Zanzibaris and all Tanzanians in general."
The preliminary death toll makes this one of the deadliest incidents of its kind in a decade.
The latest figures on passengers suggested more than 800 people were on board the stricken ferry, including families returning home after the holidays to celebrate the end of the Muslim holy month of Ramadan.
Earlier, officials had said about 600 people were believed to have been on board, but the exact number of passengers on this type of ferry is often difficult to establish as no reliable passenger lists are kept.
No foreigners have so far been reported amongst either the dead or rescued, according to an AFP reporter at the scene.
Ferries have a poor safety record in Tanzania. In May 2009, a ferry capsized leaving six people dead, while several fires on cargo boats have been reported in recent years.
Tourism is the main foreign currency earner for Zanzibar, famed for its white-sand beaches and historical buildings in Stone Town, listed as a world heritage site by UNESCO, the United Nations cultural organisation.
Pemba lies some 80 kilometres (50 miles) northeast of Unguja.