A judge in Delhi has sentenced to death four men convicted for their role in the gang-rape and murder of a 23-year-old physiotherapist in the Indian capital last year.

Bus cleaner Akshay Thakur, gym instructor Vinay Sharma, fruit-seller Pawan Gupta and unemployed Mukesh Singh were convicted earlier this week of rape, unnatural sex, murder, conspiracy and destruction of evidence. They had denied the charges against them and their lawyers have said they will appeal against both the verdict and the sentence.

The sentence was pronounced at 2.30pm by Yogesh Khanna, the judge who has heard the case over seven months at the district court of Saket in south Delhi.

It will be automatically referred to a high court bench of two judges who will consider the sentence and the appeal that lawyers for the four men have said they will file.

If upheld, an appeal to the supreme court is also possible. The Indian president can pardon offenders. Such a process would be likely to take several years.

The parents of the victim, who died from massive internal injuries caused when she was penetrated with an iron rod in the attack in December, have repeatedly called for the men to be hanged. They were in court on Friday.

Gaurav, the brother of the victim, said it had been hard to watch the accused men "laughing" during the trial and that the family were "very happy" with the sentencing.

"This is true justice for my sister," he told the Guardian.

Officials said the four men had been calm when the sentence was announced.

The father of the victim's male friend, who was with her during the attack and badly injured, said he welcomed the sentence.

"My respect for the Indian judiciary has gone up manifold. It was death they deserved and death they got," Bhanu Pratap Pandey said. Crowds outside the courthouse cheered when the verdict was announced.

Gaurav said the family would campaign for a longer sentence for the juvenile convicted in a separate trial two weeks ago.

VK Anand, a defence lawyer, said the trial had been fair but that "mitigating circumstances" should have been taken into account by the judge when sentencing.

Prosecutors have insisted that the case qualifies as "the rarest of the rare" that justifies the severest punishment. They described it as a "diabolic" act of "extreme brutality" and stressed what they said was a premeditated plan to murder the victim and a male friend by running them over after they were dumped, apparently unconscious, from the bus in which they had been assaulted.

AP Singh, representing 19-year-old Sharma, reminded the court of his client's youth and the effect of alcohol, while Thakur's lawyer argued that the 26-year-old drifter had a young son and an aged mother.

There is little doubt that public opinion firmly favours hanging. Newspapers on Friday morning reported that there was a "strong case for [the] death penalty" and the country's usually argumentative televised debates have struggled to overcome unanimity of opinions on the issue.

Colin Gonsalves, a prominent human rights campaigner, said the men should receive life sentences, not death.

"It has become a very violent and cruel kind of society. I hope the leaders would show more vision and moderation. It is sad what we have become. The mood is toxic and the judiciary will not want to be seen as out of sync with the public mood," he told the Guardian before the verdict.

The trial of five of the attackers started in February. One defendant, Ram Singh, a bus driver and the brother of Mukesh, hanged himself in prison in March. The oldest of the six men accused of the attack on the physiotherapy student, he was alleged by police to have been the ringleader. The youngest among the alleged attackers, who was 17 at the time of the assault, was tried separately and was last month sentenced to three years in a juvenile reform home – the maximum possible punishment under Indian law.

The attack provoked outrage in India and sparked protests across the country. It also led to an unprecedented national discussion about sexual violence and calls for widespread changes in cultural attitudes and policing, and legal reform. The international image of the country was damaged, with numbers of female tourists dropping significantly.

Relatives of the accused have spoken out against the verdict.

"If he would have been a politician's son this would not have happened with him," Vinay Sharma's mother, Champa, told reporters.

The prosecution case relied on testimony from 85 witnesses, a statement given by the victim before she died, DNA samples, dental records from bite marks on the victim's body that matched the teeth of some of the men and the evidence of her male friend.

The victim's friend described how the couple were attacked after boarding the bus on the way home from an evening movie at an upscale shopping mall.

The victims were eventually dumped on a roadside layby on the outskirts of Delhi, and the woman died two weeks later in a Singapore hospital. Her ashes were scattered in the Ganges river, near her ancestral village in rural India.

The men were also found guilty of robbing another man earlier in the evening of the incident.

Police described how the six had set out from the Singh brothers' home in a bus on a "joy ride". They then tricked the victim and her friend into boarding the bus and assaulted them shortly afterwards.

But though laws on sexual assault and harassment were tightened in the aftermath of the incident, serious institutional reforms will take much longer, women's rights campaigners say.

Gang-rapes, acid attacks and other acts of violence against women continue to be reported across India each day.

Police in New Delhi believe a rise in rape reports is due partly to an increased willingness by victims to come forward. There were 1,098 cases of rape reported in the capital in the first eight months of this year, more than double the number in the same period last year, according to police data. About 40% of the cases were registered in the first three months in the immediate aftermath of the 16 December incident.

Ten women on average complain of being stalked, groped or otherwise harassed in the Indian capital every day. Karuna Nandy, a supreme court lawyer and campaigner, said the focus on high-profile cases distracted from the need to reform the "nuts and bolts" of the Indian criminal justice system.

An eight-year unofficial moratorium on executions ended on 21 November 2012 with the killing of Mohammad Ajmal Kasab, a Pakistani Islamic extremist convicted of multiple murders in the November 2008 terrorist attacks on luxury hotels and other targets in Mumbai, the Indian commercial capital. It was followed on 9 February 2013 by the hanging of Mohammad Afzal Guru, convicted for a terrorist attack in December 2001 on the Indian parliament. The president, Pranab Mukherjee, has rejected 11 clemency pleas since he took office, confirming the death penalty for 17 people. His predecessor took a more lenient approach.

The sudden spate of executions has worried anti-capital-punishment campaigners.

"In the past year, India has made a full-scale retreat from its previous principled rejection of the death penalty," Meenakshi Ganguly, South Asia director of Human Rights Watch, said last month.

According to disputed official figures, there have been 52 executions in India since the country gained its independence in 1947.

Many claim that hundreds more occurred in the 1950s and early 1960s.

India has twice voted against United Nations resolutions demanding a global moratorium on capital punishment.