Union safety representatives were forced to step in after a whistleblower reported the use of “dangerous” metal weapons in a scene involving child actors on the set of the fantasy sequel Allegiant, reports the website Deadline.

Thirty young actors allegedly risked serious injury from more than 100 untrained adult extras wielding metal clubs, scythes, axes and machetes during a battle scene being shot for the film, the third episode of dystopian saga The Divergent Series.

The whistleblower, who has asked to remain anonymous, called in representatives from the International Alliance of Theatrical Stage Employees (IATSE) in Atlanta, after witnessing a chaotic “melee” on the first day of shooting the scene at an abandoned mill in rural northwest Georgia. Following the union’s intervention, the weapons, some of which were sharp, were subsequently replaced with rubber equivalents for the second day of the shoot.

The studio Lionsgate had been filming a battle sequence in which denizens of a run-down settlement known as the Fringe face off against government soldiers who have arrived to take away their children. “I had to do a double-take when the prop master passed out the weapons to the extras,” the whistleblower wrote in an email to the film’s safety consultant, seen by Deadline. “Concerned, I went around and handled the weapons for myself and saw that they were steel and aluminum, with bladed edges, and some were quite sharp.”

The email continued: “Most of the Fringe adults were given prop weapons for action scenes in which they were running around panicked as their children were kidnapped, with soldiers chasing them. The children were also running through the melee, and as the scene progressed they were breaking free and running in all directions on their own as the Fringe adults tried to stop the soldiers.

“Everyone seemed to know it was wrong, but no one was willing to speak up. To me, it seems that saving money – the expense of rubber props – took priority over safety. This particularly upset me because small children were involved. I personally saw four people trip and fall just because of the footing on the set, and several people were given medical care for heat exhaustion, which can cause fainting – and falling on these weapons is just as dangerous as swinging them into someone else during the chaotic scene.”

The production’s safety coordinator has not yet made any public comment on the claims but promised the whistleblower action via email. “Thank you for bringing this to my attention,” the unnamed coordinator wrote. “I do not and will not take this lightly. As you are well aware of, these weapons are completely unsatisfactory for the type of action that you have described. I will bring this to the attention of all key personnel involved with this production as well as Lionsgate executive staff. Thank you for your willingness to express yourself and others and I will continue to do everything I can to make our industry safer, injury and fatality free.”

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A Lionsgate spokesperson told Deadline: “We take safety issues very seriously, and we are currently investigating this.”

Safety on Hollywood film sets has emerged as a major talking point following the death of camera operator Sarah Jones on a railway track during the filming of Gregg Allman biopic Midnight Rider in February 2014. Jones died when a train struck a hospital bed placed across a track on the Doctortown trestle bridge over the Altamaha river in Wayne County, Georgia, during the filming of a dream sequence featuring the actor William Hurt as Allman.

The film’s director, Randall Miller, later received a two-year jail sentence and eight years’ probation for involuntary manslaughter and criminal trespass. The whistleblower in the new incident is said to have known Jones personally.

Allegiant, based on Veronica Roth’s third novel in the young adult Divergent trilogy, is being released in two parts. The Divergent Series: Allegiant – Part 1 is due to hit multiplexes in March next year, with part two following in March 2017.