An Indian court has sentenced four men to death after they were convicted of killing a woman they gang raped and tortured on a bus in New Delhi.

Bus cleaner Akshay Kumar Singh, gym instructor Vinay Sharma, fruit-seller Pawan Gupta and unemployed Mukesh Singh were sentenced today.

Judge Yogesh Khanna, who convicted the men for gang rape and "cold-blooded" murder earlier this week, rejected their lawyers' plea for a lighter sentence.

"Everybody got the death penalty," defence lawyer AP Singh told reporters outside the Delhi courtroom, where dozens of police had formed a barricade to keep crowds back.

The woman, a 23-year-old trainee physiotherapist, and a male friend were lured onto a bus by five men and a teenager.

The woman was then repeatedly raped and tortured with a metal bar.

Her injuries were so severe that she died two weeks later in a Singapore hospital.

One of the five men arrested in connection with the attack took his own life in prison in March.

The teenager was sentenced to three years in a reformatory last month, the maximum sentence that can be given to juveniles under Indian law.

Judge Khanna's ruling still has to be ratified by the Delhi High Court, and the four men can appeal all the way to the Supreme Court.

Lawyers said the appeals process could take years.

The case is being seen as one of the biggest tests in years of India's paradoxical attitude towards the death penalty.

Indian judges hand down on average 130 death sentences every year, but India has executed just three people in the past 17 years.

Despite its apparent reluctance to carry out the sentences, last year India voted against a UN draft resolution calling for a global moratorium on executions.

In November, India ended what many human rights groups had interpreted as an undeclared moratorium on capital punishment when it executed Mohammad Ajmal Kasab, a militant convicted for the 2008 attack on Mumbai.

Three months later, it hanged Mohammad Afzal Guru from the Kashmir region for a 2001 militant attack on parliament.

Many in India had demanded the death penalty in the case that triggered massive protests.