A 23-year-old Indian woman, whose gang rape aboard a bus in New Delhi spawned days of mass protests across India, has "taken a turn for the worse," according to a doctor who is treating her at a Singapore hospital.

The woman's vital signs are deteriorating, and there are signs of severe organ failure, Dr. Kelvin Loh, chief executive officer at Mount Elizabeth Hospital, said Friday.

Authorities haven't released the name of the rape victim, but protesters are calling her Damini, which means "lightning" in Hindi.

Her injuries were so severe that she spent days in intensive care, battling for her life, after the December 16 incident.

Police said Saturday that she had recovered enough to give a statement to a magistrate from her hospital bed the night before. But on Sunday, she underwent another surgery to wash out infection in her abdomen, her doctors said.

Reported rape cases have increased drastically over the past 40 years -- from 2,487 in 1971 to 24,206 in 2011, according to official figures. New Delhi alone reported 572 rapes last year and more than 600 in 2012.