CAPE TOWN, South Africa – Twenty people were confirmed dead on Sunday and two were in critical condition following an incident at a nightclub in South Africa’s southern city of East London.

Police said they were investigating the mystery deaths.

“The death toll stands at 20. Seventeen died at the scene and three have died in hospital. There are still two who are very critical,” head of the provincial government safety department Weziwe Tikana-Gxothiwe said on local TV.

Earlier on Sunday, 17 people were found dead at the nightclub in Enyobeni, police had said.

“We’re still investigating the circumstances surrounding the incident,” a provincial police chief brigadier Thembinkosi Kinana told AFP.

The nightclub is about 3km from the city centre.

Unverified pictures shared on social media showed bodies with no visible signs of injuries, strewn on the floor of the club as though the people died suddenly.

Police said the dead were aged between 18 and 20.

The Dispatch newspaper reported that “the patrons were either exposed to some form of poison or an incident resulted in a large number being injured and killed in a stampede.”

Local television showed police officers trying to calm down a crowd of people gathered outside the club, which lies on the Indian Ocean coast, nearly 1,000 kilometres south of Johannesburg.