Surgeons have successfully separated conjoined 15-month old sisters Nima and Dawa following almost six-hour surgery at the Royal Children’s hospital in Melbourne on Friday.

The head of paediatric surgery, Dr Joe Crameri, led the operation and said “the best part of the surgery is there were no highs and there were no lows” during it. “It was all very calm … there was calm discussion and banter,” he said.

The surgery was initially planned for October but was postponed after last-minute checks revealed the sisters were not ready because they needed extra nutritional support.

The girls were brought to Australia with their mother from Bhutan in October. They were joined at the torso and their livers were joined. But doctors in their home country did not have the surgical experience necessary to carry out the complicated operation.

“Mum is very relieved,” Crameri said, flanked by his surgical team still dressed in their scrubs. “She was very stressed today, it has been a very difficult day for her”.

Both girls have had their breathing tubes removed since the surgery which he described as an important and promising step. Neither are in intensive care.

The Victorian government has offered to pay for the procedure and recovery, expected to cost at least $350,000. Bhutan’s only paediatrician, who has long been involved in the girls’ care, travelled to Melbourne to watch the surgery. He acted as a translator throughout the procedure for the girls’ mother, who spent time praying and meditating.

The cost of the flights and accommodation was covered by the Children First Foundation, an Australian-based charity that gives children from developing countries access to specialist surgeries and medical care. More than one-third of people in Bhutan live below the poverty line.

The operation at times involved about 25 medical staff. Earlier on Friday, Crameri told the ABC the challenges of the surgery would depend on where the girls were connected, with the team unsure if they shared a bowel.

But on Friday afternoon he said once they were able to successfully separate their livers without compromising their health and access the bowel without impedement the surgery was less complicated.

“The greatest challenge was what we were going to find once we went into the abdomen,” he said.

He said the next few hours would still remain critical to their recovery. The main challenge would be the healing of wounds.

“We feel quietly confident we will have a good result but as with all post-operative cases we will be closely monitoring things over the coming hours.”