Halle Berry's new film was shut down after crew found suspected live ammunition on set.
Police raced to the set of Our Man From Jersey in London when they were alerted by workers to the potentially deadly discovery.
Scotland Yard confirmed in a statement: "Police were called to reports of an item, described as a bullet casing. It was found to be a crushed balloon gas canister and was disposed of by officers."
A source told Saturday's (May 28) Daily Mirror about the drama this week: "It was quite alarming and there was no hesitation in phoning the police, who arrived quite promptly."
Berry's new action thriller, billed as a "blue-collar James Bond", was being filmed in Camberwell Green magistrates court, South East London, when a canister of suspected arms was found.
Other locations used for filming include Kings Cross station and Albert Bridge in Chelsea, where extras have been seen dressed as armed motorcycle police, with a helicopter hovering over the structure.
Berry — who has daughter Nahla Ariela Aubry, 13, with ex Gabriel Aubry, 45, as well as eight-year-old son Maceo-Robert Martinez with former husband Olivier Martinez, 55 — will star with Mark Wahlberg, 50, in the upcoming Our Man From Jersey.
It revolves around a construction worker who is roped into the spy world by his former high school girlfriend Roxanne, played by Berry, for an intelligence mission.
The 55-year-old Oscar-winning actress, who is dating musician Van Hunt, 52, recently starred in and directed Bruised, and is set to appear in sci-fi film The Mothership, while Mark's film Father Stu is currently in cinemas.