Japanese authorities have formally declared a 20-kilometer exclusion ring around the earthquake- and tsunami-damaged Fukushima Daiichi nuclear power plant.
The order enforcing the legal no-entry zone is due to come into effect at midnight on April 22.
Chief Cabinet Secretary Yukio Edano has urged residents to abide by the order for their own health and safety, saying the Fukushima area is still unstable.
Almost all the area's nearly 80,000 residents left when the region was evacuated after the March 11 earthquake and tsunami.
But reports say some residents have been returning to their homes, and police have been unable to prevent them under the law.
AP reports that under the no-entry order, people who enter the zone without authorization could face fines of up to 100,000 yen ($1,200) and possible detention.
Authorities say they will allow residents to return to the zone for short periods of time to collect belongings but will be required to go through radiation screening.
The Fukushima plant has been leaking radiation into the air, ground, and sea since its power and cooling systems were knocked out by the twin disaster, which is the world's worst nuclear disaster since Chornobyl in the former Soviet Union 25 years ago.
compiled from agency reports