HOURS before actor Alec Baldwin fired a fatal gunshot from a prop gun that he had been told was safe, a camera crew for the movie he was filming walked off the job in protest at conditions and production issues that included safety concerns.

Disputes in the production of the Western film Rust began almost from the start in early October and culminated with seven crew members walking off several hours before 42-year-old cinematographer Halyna Hutchins was killed.

The crew members had expressed their discontent with issues ranging from safety procedures to their accommodation, according to one of those who left.

At a rehearsal on the film set at the Bonanza Creek Ranch outside Santa Fe on Thursday, the gun Baldwin used was one of three that a firearms specialist, or "armourer", had set on a cart outside the building where a scene was being rehearsed, according to court records.

The documents indicate that an assistant director, Dave Halls, grabbed a prop gun off the cart and handed it to Baldwin, indicating incorrectly that the weapon did not contain live rounds by yelling "Cold gun".

When Baldwin pulled the trigger, he unwittingly killed Hutchins and injured director Joel Souza, who was standing behind her inside a wooden, chapel-like building.

Baldwin, 63, who is known for his roles in 30 Rock and The Hunt For Red October as well as his impressions of former president Donald Trump on Saturday Night Live, has described the killing as a "tragic accident". He was a producer on Rust.

A 911 call that alerted authorities to the shooting hints at the panic on the film set, as detailed in a recording released by the Santa Fe County Regional Emergency Communications Centre.

"We had two people accidentally shot on a movie set by a prop gun, we need help immediately," script supervisor Mamie Mitchell told an emergency dispatcher. "We were rehearsing and it went off, and I ran out, we all ran out."

The call handler asked if the gun was loaded with a real bullet.

"I cannot tell you. We have two injuries," Mitchell replied. "And this (expletive) AD (assistant director) that yelled at me at lunch, asking about revisions ... He's supposed to check the guns. He's responsible for what happens on the set."

Court records say that Halls grabbed the firearm from the cart and took it to Baldwin, also unaware that it was loaded with live rounds, a detective wrote in a search warrant application.

It was unclear how many rounds were fired. Armourer Hannah Gutierrez removed a shell casing from the gun after the shooting, and turned the weapon over to police when they arrived, the court records say.

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Guns used in film-making are sometimes real weapons that can fire either bullets or blanks, which are gunpowder charges intended to produce little more than a flash and a bang.

New Mexico workplace safety investigators are examining whether film industry standards for gun safety were followed during production of Rust.

The Los Angeles Times, citing two crew members it did not name, reported that five days before the shooting, Baldwin's stunt double accidentally fired two live rounds after being told the gun did not have any ammunition.

A crew member who was alarmed by the misfires told a unit production manager in a text message: "We've now had 3 accidental discharges. This is super unsafe," according to a copy of the message reviewed by the newspaper.

The New York Times also reported that there were at least two earlier accidental gun discharges, citing three former crew members.

Mitchell, the script supervisor, told the Associated Press she was standing next to Hutchins when the cinematographer was hit.

"I ran out and called 911 and said 'Bring everybody, send everybody', " she said. "This woman is gone at the beginning of her career. She was an extraordinary, rare, very rare woman."

Film-maker Souza, who was shot in the shoulder, said in a statement to NBC News that he was grateful for the support he was receiving and "gutted" by the loss of Hutchins.

"She was kind, vibrant, incredibly talented, fought for every inch and always pushed me to be better," he said.

Santa Fe-area District Attorney Mary Carmack-Altwies said prosecutors will be reviewing evidence in the shooting and do not know if charges will be filed.

At a vigil on Saturday, around 200 film crew workers gathered for a candlelight vigil as the sun set. They shared grief at the loss of one of their own, and fear of accidents on their own film sets.

Several in attendance lit candles, held a moment of silence, read poetry and made brief comments including one testimonial to Hutchins' artistic spark and generosity.

"Her death shouldn't have happened, Union sets should be safe sets," said Liz Pecos, president of IATSE Local 480.

Production on Rust was halted after the shooting.

The crew member that spoke to the AP said he never witnessed any formal orientation about weapons used on set, which would normally take place before filming begins.

He also said only minimal Covid-19 precautions were taken, even though crew and cast members often worked in small enclosed spaces on the ranch.

The crew were initially housed at the Courtyard by Marriot in Santa Fe, according to the crew member. Four days in, however, they were told that they would be moved to the budget Coyote South hotel. Some crew members baulked at staying there.

"We packed our gear and left that morning," the crew member said of Thursday's walkout.