The information comes from the opposition party Chadema, which also announces that protests are taking place in the large city of Dar es Salaam.
Currently, the number of dead in Dar (es Salaam) is around 350 and in Mwanza over 200. If you add the numbers from other places, the total number is around 700, says Chadema spokesman John Kitoka.
A security source claims to have heard a similar number, according to AFP.
But according to the country's Foreign Minister, Mahmoud Thabit Kombo, no excessive force has been used. In an interview with Al Jazeera, Kombo says there are no figures on the number of deaths.
However, Seif Magango, spokesperson for the UN High Commissioner for Human Rights, urges Tanzanian security forces to refrain from "disproportionate force including deadly weapons" against protesters and to act to reduce tensions.
Wednesday's presidential and parliamentary elections in Tanzania were derailed by chaos and violence that has now lasted three days. Crowds are furious over the fact that President Samia Suluhu Hassan's main challengers have been either jailed or banned from participating, as well as increased repression of government critics in general.
"Our message to the government is: Stop killing our protesters. Stop police brutality. Respect the will of the people, namely a fair electoral system," says John Kitoka.
The Internet and much other communication have been shut down and it is difficult to follow what is happening.
The Swedish Ministry of Foreign Affairs advises against non-essential travel to Tanzania due to the security situation.
