The authorities in the north-eastern Nigerian state of Yobe say 471 people have died in the past five weeks, adding it is an unusually high number of deaths from health issues.
It is not clear whether the deaths are linked to coronavirus
Nigeria has so far confirmed nearly 5,000 cases of the virus, with 164 deaths.
Yobe State Commissioner for Health Muhammad Lawan Gana told the BBC that an initial investigation found most deaths were of elderly people with pre-existing medical conditions such as hypertension and diabetes.
But some had shown symptoms of coronavirus.
He said the deaths occurred in just four areas of the state.
There have been reports of hundreds of unexplained deaths across northern Nigeria in recent weeks – including in the populous state of Kano.
The authorities are cautious to link them directly to the coronavirus pandemic, saying investigations are being carried out.
Low testing rates across Nigeria are raising fears that many people might be carrying the virus undetected.