Sydney  - The second of the Bangladeshi conjoined twins that Australian surgeons separated this week is being brought out of an induced coma.

Trishna was the first to be woken and doctors at Melbourne's Royal Children's Hospital said Friday that her sister Krishna would soon follow.

"She is more alert, starting to breathe more and opening her eyes," the hospital said in a statement.

Scans of the 2-year-old orphans showed no brain damage from the 31-hour operation that began Monday.

The surgery was declared a success and there was optimism that both would make a full recovery.

Doctors estimated that the chances of both twins surviving the marathon procedure were only 25 per cent and that each had a 50-per-cent chance of avoiding brain damage.

This year attempts in Britain and Bangladesh at separating twins failed, but an operation in Saudi Arabia on Egyptian brothers was successful.

Plastic surgeon Tony Holmes, who was in the team crafting new skulls made of bone fragments and plastic parts, said Krishna had more extensive neurosurgery and had experienced more changes to her body than Trishna.

"It was hard to tell just how much of the brain tissue was crossing over," he told national broadcaster ABC "But during the operation it became apparent that the majority of the difficulty was on Krishna's side."

The twins, who turn three next month, were left in a Dhaka orphanage at birth. They have spent their last two years in Australia and will stay in Melbourne for at least two more years.

"They've got to be here for another couple of years, they're going to need a lot of additional help," Children First Foundation chief executive Margaret Smith said.

Smith said Moira Kelly, who arranged for the twins to come to Australia in 2007, would consider adopting them. "I think she'd like to do that, but that's something we can't make a decision on at the moment," Smith said.

The chance of them both making a full recovery is still only estimated at 25 per cent but without the operations they would have died within the year.

Atom Rahman, the twins' joint local guardian along with Kelly, said it was too early to say whether the pair would be returned to their Dhaka orphanage.

"There are three dimensions to the question of whether they will stay here," he said. "One is what the guardians feel about the issue, the type of medical care that is required and the legal implications of possible immigration."  (dpa)