The Precision Air plane crash landed shortly before landing at Bukoba airport due to inclement weather, authorities said on Sunday.
A domestic airline plane plunged into Lake Victoria in Tanzania early on Sunday, and the country's prime minister says 19 people on board were killed.
Prime Minister Kassim Majaliwa gave the new death toll, up from three.
A total of 43 passengers and crew are believed to have been on board the ATR 42-500 operated by Precision Air, Tanzania's largest private airline.
The aircraft crashed due to bad weather shortly before landing in the northwestern city of Bukoba, police said, adding that rescue efforts were ongoing.
“We have managed to save quite a number of people,” Kagera province police commander William Mwampaghale told journalists.
“When the aircraft was about 100 metres midair, it encountered problems and bad weather. It was raining and the plane plunged into the water,” he said.
Mwampaghale said the rescue efforts were continuing.
Local authorities said 26 of the 43 people on board the Precision Air flight from the coastal city of Dar es Salaam had been rescued.
It was not clear if any of those who were rescued died at the hospital.
Precision Air released a brief statement confirming the accident.
"An investigation team consisting of Precision Air technical staff and TAA (Tanzania Airports Authority) has also departed to join the rescue team on the ground," the airline said.
"Precision Air sincerely understands the anxiety for confirmed information and will therefore do its best to issue more details," the company said.
"The next update will be issued as soon as we receive more information from the accident scene."
The accident comes five years after 11 people died when a plane belonging to a safari company crashed in northern Tanzania.