A second Bangladeshi twin began returning to consciousness on Friday, three days after being separated from her conjoined sister in a landmark operation in Australia, the hospital said.

Krishna was opening her eyes and slowly becoming more alert as she came out of an induced coma, a statement said. Her sister, Trishna, was already awake and talking after the surgery that doctors have hailed as a success.

"Krishna is waking up slowly. She is more alert, starting to breathe more and opening her eyes," the statement from the Royal Children's Hospital said.

"Trishna continues to do well. Both girls are in a serious but stable condition."

A team of specialists worked for 32 hours on Monday and Tuesday to divide the two-year-olds' connected skulls, brains and blood vessels in a procedure that took two years of planning and preparatory operations.

Krishna is expected to make a slower recovery than Trishna, who was "100 percent perfect" after waking up on Thursday, one of their guardians said.

"I just said hello and she was doing the same thing with her arm (that she always does) ... I just knew she was 100 percent perfect," Atom Rahman told Sky News.

Trishna and Krishna were rescued from certain death in an orphanage in the Bangladeshi capital Dhaka, where doctors said they were powerless to improve the girls' fading health.

But they have been nursed back to fitness since arriving in Australia two years ago and starting preparations for this week's notoriously risky surgery, which was initially given just a 25 percent chance of complete success.

"It's a miracle we have here at the hospital... I can't comprehend, it's like being in the twilight zone," Moira Kelly, their other guardian, said through tears on Wednesday.