Nigeria’s government on Thursday warned that Africa’s most populous nation could soon see an “exponential” increase in coronavirus infections unless contacts of confirmed cases are tracked down quicker.

The country of around 190 million people has so far recorded just 51 infections and 1 death, but testing has been limited.

“We have 4,370 people of interest whom we are tracing. We urge those who have had contact with suspected cases to immediately report to the authorities,” Information Minister Lai Mohammed said.

“We are on the verge of reaching the level of community spread. We must stop this immediately or we will record exponential cases in the days ahead.”

Experts have cautioned that Nigeria is highly vulnerable to the spread of the disease given its weak healthcare system and high population density.

The country has taken a raft of measures to try to curb the virus including closing its airports and land borders, shuttering schools and telling people to stay home in key cities.

The vast majority of confirmed infections so far have been from people coming to Nigeria from abroad, but officials in economic hub Lagos have already recorded some local transmission of the disease.