Global aid agency Doctors Without Borders (MSF) has said it rejected cash for the Ebola response from Australia, asking the country instead to deploy desperately-needed medical teams to West Africa.

Canberra initially offered 2.5m Australian dollars ($2.2m), the charity said on Wednesday, before providing an additional donation of 18m Australian dollars ($16m) on Thursday.

"The government has assessed that, at this stage, financial contributions are the best and most efficient way Australia can make a rapid contribution to the global response and support front-line health services in the affected countries,'' Foreign Minister Julie Bishop said in a statement.

Australia must stop making excuses to join the fight against Ebola. - Doctors Without Borders/Medecins Sans Frontieres statement

She said that the additional donation was provided in response to a UN appeal for $50m to meet needs over the next month.

But MSF said the previous day that it had reached its logistical limitations and could not increase its assistance in Liberia, Sierra Leone, and Guinea, the three countries most affected by the epidemic which killed at least 3,000 people.

"MSF simply does not have the capacity to do this job alone. We are already turning people away from our clinics which have been stretched beyond over capacity for weeks," it said in a statement.

"Australia must stop making excuses to join the fight against Ebola."

The agency said even a small number of Australian healthcare workers would have a "very significant impact".

"Even a dozen trained staff who could oversee local teams to manage an isolation centre, help case finding and outbreak control measures would save thousands of lives today," MSF said.

Paul McPhun, the executive director of MSF Australia, warned the number of infected was doubling every three weeks.

"These are shocking statistics, yet still countries like Australia with the capacity to make a real difference on the ground are looking at each other to take responsibility, and are refusing to send their own personnel to help," he said.

"Facing this reality today, it is unthinkable that Australia is waiting for an invitation from the World Health Organization [WHO] to act."

The Australian charity Save the Children also called on Australia to follow the United States' example by sending troops.

The outbreak of Ebola, the worst on record, has infected at least 6,500 people, according to the WHO.