The World Health Organization has urged Tanzania to start reporting coronavirus cases and share its data.
Tanzania is one of the few countries in the world to not publish data on Covid-19 cases.
It last did so in May, when about 500 cases and 20 deaths were recorded. The following month, President John Magufuli declared Tanzania "coronavirus-free".
But concern is growing about the possibility of a hidden epidemic.
The WHO's plea comes after a spate of deaths of government officials.
The vice-president of Tanzania's semi-autonomous island of Zanzibar, Seif Sharif Hamad, died on Wednesday after his party said he had contracted Covid-19.
He was the most prominent politician in Tanzania to have openly declared that he had the virus.
The head of the civil service, John Kijazi, also died on Wednesday but no reason was given for his death.
World Health Organization Director-General Tedros Adhanom Ghebreyesus said in a statement: "We extend our condolences to our Tanzanian sisters and brothers on the recent passing of a senior Tanzanian leader as well as the government's chief secretary."
He then went on to urge Tanzania to start reporting Covid-19 cases and share its data.
While it is difficult to know the extent of the spread of coronavirus in Tanzania without this data, he said that Tanzanians travelling outside the country have tested positive for coronavirus.
"This underscores the need for Tanzania to take robust action both to safeguard their own people and protect populations in these countries and beyond," he said.
President Magufuli had previously played down the virus and refused to take measures to curb its spread. The health minister said earlier this month that Tanzania had no plans to vaccinate.
However, on Friday, while giving a speech at Mr Kijazi's funeral, Mr Magafuli appeared to admit that the virus was circulating in Tanzania.
He said Tanzania had defeated Covid-19 last year and would win again this year.
Then on Sunday Mr Magufuli encouraged people to wear masks to avoid infection.
But he urged people to use locally-made masks, saying without evidence that some of the imported ones were not safe.