A Liberian man who died in quarantine in Lagos was suffering from the deadly virus Ebola, Nigerian officials said Friday, confirming that the worst-ever outbreak of the virus has reached Africa's most populous country.

The 40-year-old Monrovia resident arrived in Nigeria's mega-city on Sunday and was admitted to the hospital after suffering from severe vomiting and diarrhea.

He was placed in isolation because his symptoms were associated with the virus, which has killed more than 650 people across West Africa in recent months, the worst-ever outbreak since Ebola first emerged in 1976.

"The Liberian man has died," said a source with the Lagos state health ministry who requested anonymity.

The patient's blood samples were sent to a lab in Lagos and the World Health Organization (WHO) in Dakar. Lagos officials made the official diagnosis after the results came back.

Liberia has recorded 172 cases of the disease, including 105 deaths, since the outbreak began.

Yewande Adeshina, special adviser on health for the Lagos government, said "the immediate concern was not to create panic."

She said an emergency response has been rolled out, including efforts to find "those who might have had direct contact with the man in order to prevent the risks of infection."

However, she declined to comment on what type of infection they were trying to prevent.

Lagos, a severely congested city of more than 20 million people, has terrible sanitation and a weak healthcare system.