The deadly Ebola hemorrhagic fever may have reached Nigeria, local health officials say. A Liberian man in his 40s is currently being tested for the virus in the capital city of Lagos, which is home to 21 million people, according to Reuters.

The most recent Ebola outbreak has already killed 632 people in Guinea, Liberia and Sierra Leone since February. This would be the first case in Nigeria, the most populous country in Africa.

Abdulsalami Nasidi, project director of the Nigerian Centre for Disease Control, urged Nigerians to be proactive in stopping the disease, calling it a “time bomb,” according to a Thursday report in the Nigerian Tribune. Earlier this month, he told reporters that Nigeria was not prepared to fight the disease.

The virus spreads through contact with blood or bodily fluids of infected people It's been fatal for about 60 percent of infected patients during the recent outbreak.

Sheik Umar Khan, one of the region’s top physicians who led the fight against Ebola, contracted the disease earlier this week.

Nigeria ranked among the top five countries around the world in need of better health care systems by the Borgen Project, a nonprofit focused on poverty and hunger.