A woman has died of Ebola in Liberia, months after the West African nation was declared free of the deadly virus and weeks after neighbouring Guinea also recorded a new flare-up, health officials say.

"A young lady in her early thirties died of Ebola yesterday at the Redemption Hospital," a senior health ministry official said on Friday, adding that the government was preparing to release a statement on the new case.

A hospital worker also confirmed the woman had tested positive for the disease and died on Thursday.

More than 11,300 people died over the past two years in the world's worst Ebola epidemic on record, nearly all of them in Guinea, Liberia and Sierra Leone.

Liberia was declared free of active Ebola transmission in January, but the region has seen several small flare-ups even after countries have received the all-clear.

Guinea has documented a series of new infections this month, highlighting the difficulty in stamping out the lingering epidemic.

BBC reporter James Copnall said an investigation is underway.

"Authorities are taking measures to stop the disease spreading," he said.

"The news is a blow to Liberia. People had begun to believe the disease had been overcome.

"But it is not entirely a surprise. Health authorities have warned flare ups were likely, in Liberia and elsewhere."