Five men pleaded not guilty on Saturday to charges they gang raped and murdered an Indian trainee physiotherapist, in a case that led to a shake-up of laws against sexual crimes after protests about a rising number of attacks on women.

A Reuters witness saw the men file into the court room with their faces covered, where lawyers in the case said they were read thirteen charges including murder, which carries a maximum penalty of death. They left after 15 minutes.

"After the judge read out the charges, the five pleaded not guilty and walked out" said A.P. Singh, a lawyer defending two of the accused, Vinay Sharma and Akshay Thakur.

Singh said the next hearing will be held on 5 February, when the prosecution will call three witnesses to the formal start of the trial.

A sixth person police say was part of the gang that attacked the woman and her friend is a juvenile and will be tried separately.

Police say the gang lured the 23-year-old physiotherapy student onto a bus, where they repeatedly raped and assaulted her with a metal bar before throwing her bleeding onto a highway. She died of internal injuries two weeks later.