Health authorities are on high alert after 181 people were reported to have contracted the coronavirus.
The infected people are students and members of staff of a private boarding school in Lekki area of Lagos.
Lagos health commissioner Akin Abayomi broke the news on Friday saying the cases were discovered during surveillance and case investigation in the school.
The news is coming within a week of Nigeria allowing schools and businesses reopen following weeks of lockdowns which the World Health Organisation now says could do more harm than good.
The news also comes amidst widespread protests against police brutality in Nigeria. Lekki, where demonstrators have shut down a state-run tollgate, has been a major hotspot since the protests began.
Authorities in Abuja and Lagos had warned that protesters were flouting coronavirus regulations and risking the ignition of another wave of infections.
According to the Nigeria Centre for Disease Control (NCDC), Lagos has recorded 20,433 coronavirus cases with 204 deaths and over 15,000 recoveries.
The NCDC also says the coronavirus has contributed to 1,116 deaths in Nigeria in 2020 alone.