Spain's Supreme Court considered on Friday whether to uphold a ruling that cleared five young men of gang-raping a teenager at a bull-running festival, concluding a case that triggered mass protests and calls to change the law.

The woman, who was 18 at the time, and the men, who called themselves the "Wolf Pack", have both appealed to Spain's highest court after a regional court sentenced the gang to nine years each over the lesser charge of sexual abuse.

The victim's lawyer, who says she was raped in a doorway in the early hours of the morning at the 2016 San Fermin festival, called for 15-year sentences, plus two years and nine months for robbery with intimidation for each of the accused and a further 250,000 euro ($226,000) compensation for the victim.

The Supreme Court, whose proceedings were broadcast live on national TV, was expected to reach a verdict later on Friday.

Fragments of video from the men's mobile phones taken at the scene were used as evidence in the original trial, alongside biological tests.

The regional court heard they had shared videos of the incident in a WhatsApp group and joked about it shortly afterwards.

The teenager was found crying on a bench by a couple who rang the police when she said she had been attacked.

The defendants' lawyers say sex was consensual, though the woman's lawyer says she was raped and had not fought against the men due to the shock and fear she experienced.

"Nobody can grab, throw or push anyone without applying force. They applied enough force to bend the will of the victim," a lawyer for the city of Pamplona, Victor Sarasa, told the court on Friday.

A rape charge in Spain requires a plaintiff to present evidence of intimidation or specific violence such as being threatened with a knife or dealt physical blows.

The public prosecutor agreed that there was use of violence and intimidation in the assault.

"You can't ask victims to act in a dangerously heroic way," prosecutor Isabel Rodriguez said.

"I BELIEVE YOU, SISTER"

Mass protests were organised throughout Spain after the regional court awarded the lesser sentence for sexual abuse. Thousands brandished banners that read "I believe you sister" and chanted "It's not abuse, it's rape".

Marisa Soleto, head of the Women's Foundation pro-equality group, said she hoped the Supreme Court would acknowledge that rape had occurred.

"There is a social consensus on changing the law and Spain's justice system must react to that concern ... by showing it knows what crimes against women's sexual freedom are," she said.

During the appeal process, the men were freed from jail on a legal technicality that no one can be held for more than two years without a definitive sentence, which further fuelled protests calling for tougher punishment of sex crimes.

The bull festival in Pamplona involves hundreds of people dressed in white shirts and red neckerchiefs running down narrow streets in front of fighting bulls before ending in the city's bull-ring, where bullfights take place in the afternoon.

The festival is just as famous for the drinking and revelry on the sidelines, with huge street parties, processions and firework displays. The event draws thousands of tourists from all over the world.