The Ebola epidemic is still outstripping efforts to contain it, according to doctors from Médecins Sans Frontières who have mounted most of the early response in west Africa.

Speaking to MPs from the House of Commons international development committee, MSF’s head of UK programmes said the apparent decline in numbers in Liberia did not signal the end of the epidemic.

“We are still being outpaced,” said André Heller-Perrache . ”There are far more actors on the ground but we are still being outpaced by it, with Sierra Leone being the most concerning case we have.”

Dr Javid Abdelmoneim, a UK-based doctor in emergency medicine who has recently returned from Sierra Leone where he was a volunteer with MSF, said there was “too little of everything being done in terms of intervention”.

He described how doctors in MSF’s treatment centre in Kailahun would don protective suits to meet an ambulance that could have been travelling across the country for 10 hours expecting dead bodies, which are highly infectious.

“Usually there is a patient who is dead,” he said. “There was [in one ambulance] one dead woman and two who were alive but terrified. They have watched this poor woman die a wretched death and they are thinking, ‘I’m now going to die as well.’”

Prof John Edmunds, from the London School of Hygiene and Tropical Medicine, who in September called the outbreak a potential doomsday scenario, said he would not say that the nightmare had been averted. “Things have improved dramatically in Liberia now – cases were doubling every two weeks. Now there is a turnaround and they are declining.

“The number of cases in Liberia has flattened out. The increase has stopped and come down, but we haven’t got rid of Ebola. In Guinea and Sierra Leone the rate of increase hasn’t really changed much at all.”

The improvements in Liberia have been seen as safe burials have increased in Monrovia and the numbers of treatment beds have gone up. MSF said the opening of new treatment centres could not be rushed, however. “It may take time to build something but the most critical moment is the opening of the treatment centre,” said Abdelmoneim.

Rushing things could put health and sanitation workers at risk. “The opening is always going to be slow and needs to be done safely and effectively for the sake of the healthcare workers,” he said.

Justine Greening, the international development secretary, told the committee 1,000 NHS staff had volunteered to work in west Africa, although it is thought that few, if any, have yet left the UK. “Many are now going through a process of being trained up and will be heading out to Sierra Leone,” she said. They would help staff the UK treatment centres that are being constructed.

Abdelmoneim said some may face difficulties over their absence from their usual NHS jobs. “Whether they can get the time away from their trusts and their position backfilled is an altogether different question,” he told MPs.

Edmunds said more staff were critical to the Ebola response. “There are not many UK health workers out there at the moment. There is no point opening new treatment centres if there is nobody to staff them,” he told MPs.

“This needs to be much more urgent on the part of the NHS for our own good. If we don’t stop this epidemic in west Africa, we are going to get cases in the UK.”