The grade five and six students fell from a height of about 30 feet after the inflatable was blown into the air at Hillcrest Primary School in Devonport, northwest Tasmania, at around 10 a.m. local time on Thursday. Two of the deceased were girls and two were boys.

The children were at an event to mark the end of the year at primary school. In those grades, they would be typically have been aged 10 or 11.

“These children were meant to be celebrating their last day of primary school,” Tasmania Police Commissioner Darren Hine said. “Instead we’re all mourning their loss.”

There was no immediate explanation for how the bounce house, known locally as a bouncy castle, became airborne. No other details were released about how many children were on it at the time, Australia’s ABC News reported.

Of the five children being treated at the hospital, four are in a critical condition and one is in a serious condition, police said.

One witness said he saw the jumping inflatable go up into the air.

“My wife heard a bang. It was pretty traumatic,” Bob Smith told ABC, “[We’re] a bit shaken. You don’t expect anything like that.

“The poor parents, I don’t know what they’re going to do,” he added.

Police officers were seen consoling each other as paramedics tended to victims and parents arrived at the school not knowing if their child had been affected.

Police Commander Debbie Williams said: “There is no doubt that this has been a very confronting and distressing scene,” and that counseling would be available for families and first responders.

Hine said a police investigation would take “quite some time,” and added that: “Our hearts are breaking for the families and the loved ones, schoolmates, teachers of these young people who were taken too soon.”

Australian Prime Minister Scott Morrison described the events as “just shattering.” He said in a news conference that for such a “horrific tragedy” to occur when young children are on a fun day out with their families “just breaks your heart.”

Tasmanian Premier Peter Gutwein said it was “inconceivable that this shocking tragedy has occurred” and promised a full investigation.

“I know that this is a strong and caring community that will stand together and support one another,” he added.

Newsweek has contacted Tasmania Police for further comment.

Update 12/16/21 at 3:30 a.m. ET: This article has been updated with further information throughout.