Extremely rare conjoined twins from Sydney, Australia, who mesmerised the world after they were born three weeks ago, have died.

Faith and Hope, who had one body and one head but two identical faces were born on May 8.

Parents Simon Howie and Renee Young were warned the odds for the babies' survival looked bleak when doctors discovered their condition, called diprosopus, during a routine ultrasound at 19 weeks.

The couple, however, went against medical advice deciding to go ahead with the pregnancy. Doctors were said to be amazed after their birth the babies managed to breathe on their own and remained in a stable condition.

But a hospital spokesman confirmed they died after 12pm on Tuesday at Westmead Children's Hospital in Sydney.

"Our precious baby girls, who gave it a good fight, are headed to the arms of the angels who will give them their wings," the couple said in a statement.

There are about 35 similar cases of diprosopus recorded worldwide with none of the babies surviving.

Speaking previously on the Australian TV programme, A Current Affair, which followed the birth, Young said: "If I only get two days with the baby I only get two days. I'll at least have some time with her."