Surgeons on Sunday entered the third tense day of a nonstop operation to separate 10-month-old Siamese twin girls from Nepal whose brains are partially fused. 

"They are still working," Singapore General Hospital communications manager Ho Lai Fung said. "Nobody can tell" when the surgeons will finish, she said. 

Ganga and Jamuna Shrestha, who come from a poor family on the outskirts of Katmandu, share the same brain cavity. Their brains share some of the same blood vessels, making the surgery extremely difficult and dangerous. 

Doctors have said that the operation, which started at 4:00 p.m. Friday, could take more than 40 hours to complete. Details will likely be released later in the week, hospital officials said. 

The doctors conducting the operation were a "multidisciplinary team" consisting of a neurosurgeon, a plastic surgeon and others, Fung said. Two teams of surgeons were working around the clock, taking turns at brief rest breaks. 

The first phase of the surgery was successfully completed early Saturday, said M.N. Swami, Nepal's honorary consul general in Singapore. He gave no details about what the first phase of surgery entailed. 

Meanwhile, Ganga and Jamuna have become celebrities in Singapore, where they have lived for six months while doctors prepared them for the surgery. 

Newspapers in the affluent city-state have described the development of the girls' distinct temperaments, reporting their first smiles and different food preferences. 

Singaporeans have donated $358,000 to help the girls. The hospital has waived many of their charges, and national flag carrier Singapore Airlines paid for the girls, their parents and their grandfather to make the trip from Nepal. 

The family has been living with the Nepalese Gurkha community in Singapore since their arrival. The Gurkhas, who come from Nepal, are famous for their service as a special group within the British military. In Singapore, they work as a special force with the police. 

Singapore is proud of its reputation as one of Asia's most modernized countries and has sought to become a hub of high-tech services, from financial to medical.