Touted as the first nuclear radiation disaster-themed blockbuster production from Hong Kong, the film revolves around an accidental radioactive leak in the city which puts the lives of seven million citizens at risk.

[2][3] In 1996, Financial Secretary Simon Fan (played by Andy Lau) loosens container inspection regulations, allowing unscrupulous traders to exploit loopholes to import dangerous goods.

Tropical Storm "Murphy" is looming, which means that radiation could spread across Hong Kong within 24 hours, putting seven million people in grave danger.

Meanwhile, fire station officer Lai Kit-fung (played by Bai Yu) and his teammates are dispatched to the unknown front line, unaware that there may be more behind this disaster than meets the eye.

Producer and star Andy Lau also appeared via a pre-recorded video discussing his role as a radiation crisis expert, as well as production of disaster spectacles and themes of humanity.

[5] On 19 July 2024, Karen Mok revealed that she had to memorise many professional terms for her role and will start working on promotions by the latter half of the year.

[10] James Marsh of Deadline Hollywood praises Anthony Pun's cinematography, noting its visual coherence and ultimately writes Cesium Fallout bombards its audience with a cacophony of mindless destruction and muddled messaging, yet somehow fails to illustrate just what it is that these individuals are so courageously fighting for.

[25] Edmund Lee of South China Morning Post gave the film 3.5/5 stars, calling it "immersive and engaging" and praising its logical narrative and "solid performances", while noting that despite some contrived plot elements, it effectively balances action and drama in its thoughtful exploration of a nuclear crisis.

[27] Yasmin Zulraez of The Sun gave the film 7/10 and praised it as a "roller-coaster ride filled with tension, heroism and the kind of emotional weight that grips the heartstrings", highlighting the film's effective combination of intense action with emotional depth, with strong performances and exploration of themes like redemption and personal conflict, despite some melodramatic moments.

[28] Whang Yee Ling of The Straits Times gave the film 3/5 stars, describing it as "big, unsubtle entertainment" that critically examines government indecision and delivers a "tense" apocalyptic spectacle effectively highlighting the dangers of man-made disasters, though she found the crisis ultimately "exhausting".