The still unexplained deaths of the teens, some of whom were celebrating the end of school exams and others a birthday party, have brought an outpouring of grief and shocked a country accustomed to injuries linked to a binge drinking culture.
"We are so heartbroken, guys. We lost one of our family members, a child who was doing grade 12 (final year) this year. We can't accept it," Yandiswa Ngqoza, an aunt, said as she choked back tears outside the morgue dressed in black attire.
"By the look of the child she has no visible injuries," Ngqoza said, before finally breaking down sobbing.
Minutes earlier she had entered the morgue and identified her niece, whose name she did not reveal.
Eastern Cape police spokesman Brigadier Tembinkosi Kinana told Reuters that the youngest of the victims at the Tavern in the city of East London was a 13-year-old girl.
Pictures circulating on social media, still unverified by the authorities, showed the bodies of youths lying scattered across the floor of the tavern, some also seen motionless on tables and couches.
Addressing a crowd outside a mortuary in East London on Sunday, an emotional Police Minister Bheki Cele had to pause speaking as he started weeping, triggering a chorus of cries among his audience.
"It is either something they ingested which will point to poisoning, whether its food or drinks, or it is something they inhaled," Unathi Binqose, spokesman for the Eastern Cape's provincial community safety department said by telephone on Monday.
He said hookah pipes were visible in CCTV footage of the scene.
"We are ruling out a stampede completely," he added, after initial media reports suggested this might be a possible cause of the deaths.
Police said 21 had died, one fewer than originally thought.
Authorities are expected to produce a toxicology report as part of the investigation.
President Cyril Ramaphosa said on Sunday he was worried about the circumstances under which young people, at least some under the age of 18 years, were allowed to gather at the tavern.
It is illegal to serve drinks to under-18s in South Africa.
The tavern had its liquor license revoked on Monday, Mgwebi Msiya, spokesman for the Eastern Cape Liquor Board, said.
"We want them to stop trading immediately," he said.
