ABUJA -?Nigeria is investigating a "strange disease" that is fast spreading in the north central state of Kogi, officials have said.

The disease, whose symptoms include diarrhea, blood-stained vomiting and high fever, had killed up to 50 people as of Friday, Nigeria's English newspaper The Guardian reported Friday.

Investigators said the disease broke out about three weeks ago. The first case was confirmed to involve a young child, who died earlier this week.

So far, three villages in Yagba West local area of Kogi State have been afflicted by the disease and locals have expressed worry that a further spread was imminent.

Local medical officials said diagnosis had proved the disease was not Lassa fever, a hemorrhagic disease that often breaks out in the West African country.

"We are sure it is not Lassa fever, but our concern is that we do not know exactly what is happening. We have not arrived at a definitive diagnosis," said Jannette Hathorn, a medical consultant who led state officials to the affected communities on Thursday.

Officials of the World Health Organization (WHO) had taken blood samples of victims, Harthorn told officials and reporters.

Saka Audu, the Kogi State commissioner for health, described the situation as "serious," saying the government will take full responsibility of the sick so as to arrest the spread of the disease.

"We are digging into the real cause of this ailment. All hands are on deck toward unraveling the definitive cause of the mysterious deaths, especially among the kids," the official said.