Alec Baldwin was rehearsing a scene that involved pointing a prop gun at the camera lens when he fatally shot cinematographer Halyna Hutchins, US media reported, citing an affidavit recording his director's account of the tragedy.

Director Joel Souza, who was standing behind Hutchins when the gun fired, said he heard what "sounded like a whip and then loud pop", according to the affidavit released to US media on Sunday.

Souza said Baldwin was "sitting in a pew in a church building setting, and he was practising a cross draw. Joel said he was looking over the shoulder of Halayna" when he heard the gunfire, NBC News reported the affidavit as saying.

US actor Alec Baldwin. Photo: Angela Weiss/AFP

It quotes Souza as saying he remembered Hutchins "complaining about her stomach and grabbing her midsection".

"Joel also said Halayna began to stumble backwards and she was assisted to the ground," the affidavit said, according to NBC. "Joel explained that he was bleeding from his shoulder and he could see blood on Halayna."

Hutchins, 42, was struck in the chest when Baldwin fired the prop gun he had been told was safe on the set of low-budget western Rust in New Mexico on Thursday. She was declared dead in hospital hours later.

Souza, 48, was treated by doctors and sent home.

Police are still investigating the shooting and have executed a search warrant at the set.

Baldwin has been interviewed by detectives in Santa Fe, and has said he is co-operating fully with the probe.

Attention has also focused on the film's assistant director, Dave Halls, who handed the weapon to the actor, and on the armourer, 24-year-old Hannah Gutierrez-Reed.

No one has been charged and no arrests have been made.

The incident happened after a lunch break, Souza reportedly said in the affidavit, adding that he wasn't sure if the gun had been checked again for safety after the break.

Security guards stand at the entrance of Bonanza Creek Ranch in Santa Fe, New Mexico, on October 22, 2021. Photo: Anne Lebreton/AFP

A camera operator also reportedly said the incident was not caught on film as the cast and crew were still preparing for the scene.

The new details emerged as Hutchins' shocked friends and colleagues gathered to pay tribute to her Sunday at a vigil where their anguish and anger were on display. 

Calls were growing for a ban on live firearms on movie sets, with a petition gathering more than 20,000 signatures and a California lawmaker announcing he would push a bill banning live ammunition on sets in the state.