Chief Cabinet Secretary Yukio Edano said the order, to take effect at midnight, was meant to prevent unrestricted entry into the mostly deserted area ordered evacuated after last month's tsunami and earthquake wrecked the Fukushima Dai-ichi plant's power and cooling systems.
He gave no details of penalties for violating the order.
"We beg the understanding of residents. We really want residents not to enter the areas," Edano said. "Unfortunately, there are still some people in the areas."
Officials said the order was meant to limit exposure to radiation leaking from the plant, and to control entry to prevent theft.
Edano said authorities would arrange brief visits for residents, allowing them to return for about two hours to collect necessary belongings. Residents would be required to go through radiation screening, he said.
Prime Minister Naoto Kan was visiting the region today to meet local officials and evacuees to discuss the plans for strict enforcement of the evacuation zone.
Almost all the area's nearly 80,000 residents left when the area was evacuated on March 12, but some have been returning and police could not legally block them.
