Doctors said the victims, aged between 18 and 29, tested positive for methamphetamine, amphetamine, ecstasy, and marijuana.
The Ministry of Health reported earlier that five had died at E Hospital, a public general hospital, and two at the Hanoi Heart Hospital while five were comatose.
Le Ngoc Thanh, the director of E Hospital, said of the three comatose patients being treated at his hospital, one is in the recovery room after coming out of the coma while the other two remain in the emergency room.
Dr Nguyen Trung Nguyen of Bach Mai, Hanoi's leading public hospital, said two patients had been transferred to the hospital in critical condition on the night of the incident, with kidney failure and cardiovascular collapse. One of them is now out of the coma and in stable condition, and can now talk, he said.
At the scene of the Vietnam Electronic Music festival at the West Lake Water Park in Tay Ho District, balloons containing nitrous oxide, commonly known as laughing gas, and unidentified pills were found, police reported.
Dubbed the biggest electronic music event ever in Vietnam, it had featured top DJs like Ben Nicky, Yellow Claw and Headhunterz, drawing thousands of fans.
Hanoi on Monday announced to suspend all music festivals until further notice, as it is investigating the cause of the deaths from the Sunday event. The incident is "especially serious," a police officer said.
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