Five men accused of the gang-rape and murder of an Indian student pleaded not guilty Saturday in a case that has sparked huge protests and led ministers to back tougher penalties, including death, for rapists.

The 23-year-old physiotherapy student was brutally assaulted in mid-December on a New Delhi bus she had boarded with a male companion as they returned home from watching a film.

The trial of the five men on charges that include murder, rape and kidnapping is being held in a fast-track court in Delhi set up to deliver speedy justice following public anger over the case.

A sixth suspect faces trial in a juvenile court.

"All five have pleaded not guilty and want the trial to continue," defence lawyer V.K. Anand told AFP outside the court.

The five men were surrounded by heavy security and rushed into the court building, their faces concealed with scarves. They remained in the courtroom for around 10 minutes before being escorted out.

The court will start hearing evidence in the case from witnesses next Tuesday, the lawyer said. A defence lawyer said earlier in the week that verdicts for the five men would be handed down "very soon".

Prosecutors say they have DNA evidence linking the defendants to the attack, as well as the victim's hospital-bed declaration and testimony from her 28-year-old companion who took part in identification parades after the ordeal.

The case sparked violent street protests across India with demonstrators demanding better safety for women and making impassioned calls for harsher punishments for rapists.

The appearance in court of the men -- aged between 19 and 35 -- came a day after India's cabinet backed harsher punishments for rapists, including the death penalty.

A government-appointed panel recommended the changes after the death of the women, who spent nearly two weeks fighting for her life before succumbing to her injuries in a Singapore hospital where she was flown for last-ditch treatment.

The changes, expected to be approved by President Pranab Mukherjee and become law as early as this weekend, include doubling the minimum sentence for gang-rape and imposing the death penalty when the victim is killed or left in a vegetative state.

"We have taken swift action and hope these steps will make women feel safer in the country," Law Minister Ashwani Kumar told reporters.

The legislation was consistent with the "sensitivities of the nation in the aftermath of the outrageous gang-rape," he added.

On Saturday, the gang-rape victim's brother praised the cabinet's decision, calling it a "positive initiative", according to the Press Trust of India.

While Mukherjee's approval will mean the changes become law, they also need to be ratified by parliament at a later date otherwise they will lapse.

Under the changes, the minimum sentence for gang-rape, rape of a minor, rape by policemen or a person in authority will be doubled to 20 years from 10 and can be extended to life without parole.

Under the current law, a rapist faces a term of seven to 10 years.

The cabinet has also created a new set of offences such as voyeurism and stalking.

India says it only imposes the death penalty in the "rarest of rare cases". Three months ago, it hanged the lone surviving gunman from the 2008 Mumbai terror attacks -- the country's first execution in eight years.