Cricket Australia has apologised to the India team and launched a probe into allegations that visiting players were racially abused by part of the crowd at Sydney Cricket Ground.
The Indian team lodged an official complaint after play on Saturday, after bowlers Jasprit Bumrah and Mohammed Siraj complained of hearing racist slurs while fielding near the boundary rope.
On Sunday, Siraj approached the umpire pointing towards the stands and the action was paused, as police ejected six fans from the ground.
CA has launched a parallel investigation with New South Wales Police, promising to take the "strongest measures" against anyone found guilty of vilification.
"It is most regrettable that an otherwise excellent test match, contested in tremendous spirit by two friendly rivals, has been tarnished by the actions of a small number of spectators over the past two days," integrity and security head Sean Carroll says.
"As hosts, we once again apologise to the Indian team."
Venues New South Wales, which operates the stadium, says CCTV footage is being reviewed to assist the investigation, and any fans identified as engaging in racial abuse will be banned from the SCG and other major stadiums in Sydney.
India's Ravichandran Ashwin says the team has been insulted by Sydney spectators in the past, but the racial abuse has crossed a line during the ongoing match, played in front of a reduced crowd of less than 10,000.
"It is definitely not acceptable in this day and age," Ashwin says. "This must definitely be dealt with iron-fist and we must make sure it doesn't happen again."
India's regular captain Virat Kohli was fined half of his match fee in 2012 for responding to barracking from the SCG crowd by gesturing at them with his middle finger.
Kohli, who returned home after playing in the first test to attend the birth of his first child, says racial abuse was completely unacceptable.
"Having gone through many incidents of really pathetic things said on the boundary lines, this is the absolute peak of rowdy behaviour," Kohli tweets. "It's sad to see this happen on the field.
"The incident needs to be looked at with absolute urgency and seriousness, and strict action against the offenders should set things straight for once."
Australia coach Justin Langer has joined the condemnation.
"It's upsetting and it's disappointing," he says. "It's one of my greatest pet hates in life that people think they can come to a sporting event, and abuse or say whatever they like.
"I hated it as a player and I hate it as a coach. It's really sad to see it happen in Australia."
The International Cricket Council says the Indian team had informed match referee David Boon of the alleged racial abuse on Saturday and the governing body is "incredibly disappointed" with the incidents at the SCG.
Under the ICC's anti-discrimination policy, CA must investigate the incident and submit a report to the Dubai-headquartered body within two weeks.
"We will provide Cricket Australia and the relevant authorities with our full support in any ensuing investigation, as we will not tolerate any racism in our sport," ICC chief executive Manu Sawhney says.
A man was banned from attending cricket matches in New Zealand for two years, after abusing West Indian-born England fast bowler Jofra Archer during a 2019 tour.