The worst-ever Ebola epidemic in the world has been officially declared over as the World Health Organisation gives all-clear for Liberia.

The end of active transmission was announced after "two 21-day incubation periods" since the last known Ebola case in the West African country was tested negative, said reports.

However, UN has warned of flare-ups of the virus in the future as the disease had re-emerged previously after Liberia was declared Ebola-free twice before, as per WHO official website.

The country was first declared free of Ebola transmission in May 2015, but the virus was re-introduced twice since then, with the latest flare-up in November.

Sierra Leone was declared Ebola-free on 7 November, while Guinea on 29 December 2015.

"WHO commends Liberia's government and people on their effective response to this recent re-emergence of Ebola," said WHO Liberia representative Dr Alex Gasasira. "The rapid cessation of the flare-up is a concrete demonstration of the government's strengthened capacity to manage disease outbreaks. WHO will continue to support Liberia in its effort to prevent, detect and respond to suspected cases."

Strong surveillance and response systems will be critical in the coming months as some of the survivors might be still vulnerable despite recovering completely.

The survivors have also been made aware of the necessary precautions to prevent any reoccurence.

The world's worst ever Ebola outbreak has claimed over 11,000 lives with the highest death toll recorded in Liberia (4,809), followed by Sierra Leone (3,955) and Guinea (2,536).