Another person who was among those found unconscious during a concert in Pasay City expired while undergoing treatment at a hospital.
A report on GMA News' 24 Oras Weekend identified the fatality as Kim Migawa, 18.
Four people, including an American citizen, were earlier reported to have died after they lost consciousness while attending an overnight concert at the open parking area of SM Mall of Asia in Pasay City in the wee hours of Sunday.
Police: 4 dead, 1 in critical condition after being found unconscious during a concert party early this morning in a mall in Pasay— Tricia Zafra (@triciazafragma7) May 22, 2016
MORE: Isa sa apat na namatay ay Amerikano. Nakikipag-ugnayan na ang mga pulis sa US Embassy. @dzbb— James Agustin (@_jamesJA) May 22, 2016
The American was identified as Eric Anthony Miller, 33 while the other fatalities were Bianca Fontejon, 18; Ariel Leal; and Lance Garcia, a businessman from Pasig City.
Fontejon and Miller were declared dead at the Manila Doctors' Hospital while Leal and Garcia expired at the San Juan de Dios hospital.
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 Agence France-Presse.
"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 rumors spreading on social media.
Reports said the victims were among those found unconscious at the open parking space where the concert was held.
The concert started at 3 p.m. Saturday and was supposed to end at 3 a.m. Sunday.
Hours after the concert started, several people were found unconscious in the concert area, where several concessionaires were allowed to sell food and other items.
Police said they received reports of the incident at around 5 a.m.
Authorities have yet to determine the cause of death of the victims.
MORE: Hindi pa matukoy ang ikinamatay ng mga biktima. Nasa Pasay Police na rin ang ilang opsiyal ng Southern Police District. @dzbb— James Agustin (@_jamesJA) May 22, 2016
In a statement, the organizers said that it was "deeply saddened" by the unfortunate event.
An announcement from the Closeup Forever Summer organizers. pic.twitter.com/cE7G1P4ot9— Closeup Philippines (@CloseupPH) May 22, 2016
"We regret that despite the very stringent measures and precautions we have put in place to ensure the safety and security of all attendees involved, this incident still transpired," Close Up said.
"As such, strict protocols were followed to immediately provide medical assistance, as well as rush all those involved to the nearest hospital where they can receive emergency care."
"We extend our deepest sympathies to the families of those who've passed away, and commit support in their time of bereavement," it added.
Close Up is also extending assistance to the other victims who are still in the hospital.
"Likewise, our efforts are now focused on supporting those needing medical assistance so they may fully recover," it said.
It added: "We are fully cooperating with the authorities in the ongoing police investigations."
Annie Garcia, president of SM Supermalls, also issues a statement expressing "our sympathies towards the unfortunate incident".
"We are assisting the event organizers, Close Up Phil., its agencies, and the authorities in the investigation," her brief statement read. — ALG/APG, GMA News