The Chateau stage was destroyed when severe storms uprooted several trees and caused them to crush the platform. A second stage was also damaged by trees.
Pukkelpop organisers confirmed early on Friday morning that the entire event has now been cancelled, saying in a statement: "Pukkelpop is in deep mourning. We truly sympathise with the families and friends of the victims.
"Words are not enough. We have struggled with the decision to continue the festival. Therefore we have decided to cancel Pukkelpop 2011. What has happened is very exceptional and could not have been predicted. We are deeply moved by all the spontaneous support the festival goers and the organisation have received."
The statement continued by emphasising that the decision to cancel the festival was "extremely difficult". Organisers also encouraged festival attendees to return home "calmly", promising extra buses and trains to help people leave the site.
Festival bosses had originally hoped to proceed as planned on Friday morning after safety checks.
Hugo Simons, the head of emergency medical planning for nearby town Hasselt, told local radio on Thursday night that three people had died, 11 are seriously injured, and another 60 have sustained light injuries as a result of the storm. The number of fatalities was revised to five early on Friday morning.
Indie rock band Smith Westerns were performing on the stage in question at the time of the collapse, and the band took to Twitter to recall what happened.
Meanwhile, Jared Leto, the frontman for 30 Seconds to Mars, also tweeted about the severe weather, writing: "CRAZY STORM AT PUKKELPOP IN BELGIUM - NOT SURE WE WILL BE ABLE TO GO ON STAGE - STAY TUNED. SAFETY FIRST."
Leto was due to play the main stage later on Thursday evening.
Last weekend, a stage collapsed at the Indiana State Fair shortly before country duo Sugarland were due to perform. Five people were killed in the accident, with dozens more injured.
Sugarland recently announced that they plan to play a memorial concert for the victims of the Indiana stage collapse, saying that they want to honour those fans who died.