Five people, including teenagers, died from unknown causes during a pop concert in a suburb of the Philippine capital, police said Sunday.

The five were among an estimated 14,000 attending the ‘Closeup Forever Summer’ open-air concert, headlined by Belgian DJ duo Dimitri Vegas and Like Mike late Saturday, investigating officer Giovanni Arcinue told AFP.

Among the fatalities was a 33-year-old foreign man, believed to be American, said Arcinue.

‘They just collapsed individually. They did not know each other. They were all in different places at the time,’ he said.

He said the cause of their collapse was still unknown although police were looking at possible heatstroke or dehydration as the country is sweltering under high temperatures brought on by the El Nino weather phenomenon.

He also said it was too early to say that the deaths were caused by drug-laced drinks, despite rumours spreading on social media.

Closeup, a major toothpaste company, issued a statement saying: ‘We regret that despite the very stringent measures and precautions that we have put in place to ensure the safety and security of all attendees involved, this incident still transpired.’

The company said it was cooperating with authorities in the investigation.