HANOI (AFP) - Seven people have died and five others are in a coma after taking drugs at a dance music festival in Hanoi late on Sunday (Sept 16), officials said, as investigators worked to identify the substance.

The victims, who were all Vietnamese, "all tested positive for drugs", deputy director of Hanoi police Nguyen Van Vien told reporters on Monday.

"Police are trying to figure out what type of drug it was," he added.