Shortages of trained staff, operational partners and funding are causing a bottleneck in efforts ‌to expand the Ebola response in the Democratic Republic of Congo as the outbreak spreads geographically, a World Health Organisation (WHO) official said on Tuesday.

The outbreak has spread beyond its initial epicentre in Bunia, affecting six provinces and prompting authorities to adopt a more decentralised strategy by building treatment centers ​closer to newly affected communities, the WHO said.

Congo's outbreak of the Bundibugyo species of Ebola has killed 3,175 ​people and infected more than 6,000, according to the WHO — making it the country's worst epidemic — ⁠and it is continuing to spread across its northeast.

WHO technical officer Luca Fontana said nearly 1,400 treatment beds had already been ​established across 59 treatment centres, one of the fastest scale-ups he said he had witnessed, including during the 2014 to 2016 ​West Africa Ebola epidemic.

"Yet, despite this extraordinary effort, we estimate that another 1,600 beds will be required," he said.

WHO estimates around three health workers are needed for each Ebola patient bed, meaning around 9,000 staff would be required for the planned capacity of 3,000 beds.

That would require the ​recruitment and training of roughly 5,000 additional health workers.

"Every time a healthcare worker walks inside the patient's area, wearing the full ​gear, the personal protective equipment, it's approximately $25. We have hundreds of staff walking inside the patient's area every single day," Fontana said.

Compounding the ‌challenge, the ⁠pool of international organisations capable of running Ebola treatment centres is limited, partly due to the impact of broader global donor funding cuts, Fontana said.

"Where are all the organisations that were running treatment centres in West Africa outbreaks in 2014 to '16? Why they are not currently in the field to support this current response is probably because of lack of resources, and this ​is probably one of the bottlenecks ​now that can delay ⁠the scale-up plan," he said.

It costs approximately $500,000 to run a treatment centre of 50 beds, according to WHO estimates.

WHO estimates that only five or six major organisations have the expertise and capacity ​to set up and operate a treatment centre for Ebola and that they risk becoming ​tied up managing ⁠existing centres unless other partners step in to take over facilities that are already running smoothly, he said.

In some cases, Congo's Health Ministry is assuming responsibility for centres opened at the start of the outbreak, but Fontana warned that its capacity would also eventually ⁠be stretched.

"So ​more actors in the field will be needed to ensure that the ​most experienced partners can move to the front line again," he said.

The WHO has urged donors to increase funding and accelerate contributions to fund the Congolese government-led ​Ebola response plan of $1.3 billion over the next six months.