Authorities are still trying to determine what killed 21 young people inside a popular bar, the Enyobeni Tavern, in the southern city of East London. Some died later in hospital.
South African authorities said on Monday the youths were probably killed by something they ate, drank or smoked, ruling out the earlier-touted possibility of a stampede.
"It is either something they ingested which will point to poisoning, whether its food or drinks, or it is something they inhaled," Unathi Binqose, spokesperson 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.
They bore no visible signs of injury, sparking speculation among local officials and politicians that this was a case of under-age drinking that went tragically wrong.
Autopsies are being conducted to see if the deaths could be linked to poisoning.
"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.
"Post-mortems (were) completed by last night and the bodies will be released to their families today," said Yonela Dekeda, provincial spokeswoman for the health department.
Forensic analysis will be conducted this week.
"Samples were taken and were on first flight to Cape Town, where the tests will be conducted," said Unathi Binqose, a government official on safety.
Special investigators from Pretoria were rushed to the scene.
Many of the victims are thought to have been students celebrating the end of their high-school exams, officials said.
President Cyril Ramaphosa is among those who have voiced concern about the incident and underage drinking.
The teenagers reportedly "gathered at a venue which, on the face of it, should be off-limits to persons under the age of 18," he said.
This report was sourced from information provided by Reuters and Agence France -Presse