The threat of a nuclear attack on California is real enough that a regional task force circulated a document to help the state prepare for a “catastrophic” strike.

Circulated by a Joint Regional Intelligence Center that encompasses southern California, the August advisory - first reported by Foreign Policy - warns of “devastating casualties and critical infrastructure damage” in the event of a nuclear strike.

Far from a Cold War relic, the document underscores the concrete risks as North Korea continues to defy the world by displaying its military prowess and threatening neighbors. It notes that North Korea tested an intercontinental ballistic missile that “appeared capable of reaching the West Coast of the United States” and that North Korean propaganda videos depict an annihilated San Francisco.

The joint intelligence center did not follow up on a request for comment. A spokeswoman for the Los Angeles Emergency Management Department said the city has been preparing for a nuclear attack for years but acknowledged that “public interest in how to respond to a nuclear attack has spiked” in recent months.

“We all know there’s a lot of talk about North Korea and the nuclear threat”, spokeswoman Kathleen Hutton told the Independent. “With the increased attention and threat, we’ve been looking at those plans to see if there’s anything more we can to do be operationally more ready”, she added.

The 16-page memo is dated August 16, 2017. In the weeks since that date, a highest-stakes geopolitical standoff has only intensified as North Korea fired multiple missiles over Japan, tested what was likely a hydrogen bomb and called Donald Trump’s threat to destroy North Korea an act of war.

Trump: US's military solution for North Korea would be 'devastating'

A nuclear blast would overwhelm the government’s capacity to respond, with federal help likely not materializing for days and first responders crippled by “significant casualties and destruction of critical infrastructure”, the document warns. Bridges and roads could be rendered unusable, as could electricity and communication infrastructure. While frightened residents would need to seek shelter and then be evacuated, the anxiety-wracked population might not follow orders. Sealed food would be safe; breast milk could be contaminated.

The document includes a primer on different types of explosions and radiation, offers tips for avoiding radioactive fallout by covering the mouth and nose or seeking underground shelter - brushing off dangerous particles and disrobing also works - and explores a RAND Corporation case study finding a bomb detonated at the bustling Port of Long Beach, south of Los Angeles, could kill 60,000 people and set off a stampede of six million evacuees.

In pictures: North Korea military drill Show all 8 1 /8 In pictures: North Korea military drill In pictures: North Korea military drill North Korea's leader Kim Jong Un watches a military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) is seen in this handout photo by North Korea's Korean Central News Agency (KCNA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) is seen in this handout photo by North Korea's Korean Central News Agency (KCNA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) KCNA/Handout via REUTERS In pictures: North Korea military drill This image made from video of still images broadcast in a news bulletin by North Korea's KRT, shows what was said to be a 'Combined Fire Demonstration' held to celebrate the 85th anniversary of the North Korean army, in Wonsan, North Korea. KRT via AP Video In pictures: North Korea military drill This image made from video of still images broadcast in a news bulletin by North Korea's KRT, shows what was said to be a 'Combined Fire Demonstration' held to celebrate the 85th anniversary of the North Korean army, in Wonsan, North Korea. KRT via AP Video In pictures: North Korea military drill This image made from video of still images broadcast in a news bulletin by North Korea's KRT, shows what was said to be a 'Combined Fire Demonstration' held to celebrate the 85th anniversary of the North Korean army, in Wonsan, North Korea. KRT via AP Video

Such preparations are not new. Ms Hutton pointed to a 2010 drill for a nuclear detonation conducted under the auspices of a planning exercise called Operation Golden Phoenix. The document notes “significant planning and exercise efforts for a nuclear attack” have unfolded for years among communities covered by the intelligence center. A state emergency plan prescribes responses to “nuclear incidents”, though that mostly covers power plant failures.