Dozens of bodies were discovered in a Sierra Leone hospital on Wednesday after an Ebola outbreak went unreported by health officials.

By the time the World Health Organisation (WHO) was called in, 87 people were dead, and the virus had hit eight of the area's 15 chiefdoms.

The WHO response team arrived on Wednesday, and what they found was disturbing. "They uncovered a grim scene," the agency said in a statement.

The local hospital had curtained off a section of the facility where 25 bodies were found. The organisation buried 87 people in 11 days, "including a nurse, an ambulance driver, and a janitor drafted in to removing bodies as they piled up."

The district had only reported 119 Ebola cases through December 9, and only 24 cases were reported last week. Over 350,000 people live in Kono District.

"We are only seeing the ears of the hippo," feared Sierra Leone Director of Disease Prevention and Control Dr Amara Jambai.

Sierra Leone recently overtook Liberia as the country with the highest number of reported Ebola cases with 7,897 infections since the outbreak began early this year.

However, Liberia reported 3,177 deaths from the virus, while Sierra Leone reported just 1,768.

Sierra Leone Health Minister Abu Bakarr Fofanah said that only laboratory-confirmed deaths are being recorded by the West African nation.

"It is difficult to put an exact figure on the deaths," he told Reuters. "They are adding suspected cases, so that is causing the discrepancies in the results. We are going by the textbook."

As of December 7, over 6,000 people have died from the Ebola outbreak that began in Guinea this spring. There have been nearly 18,000 confirmed or suspected cases of Ebola infection this year.