TOKYO -- Radiation cleanup in some of the most contaminated towns around Fukushima's nuclear power plant is far behind schedule, so residents will have to wait a few more years before returning, officials said Monday.

Environment Ministry officials said they are revising the cleanup schedule for six of 11 municipalities in an exclusion zone from which residents were evacuated after three reactors at the Fukushima Dai-ichi nuclear power plant went into meltdown following the March 2011 earthquake and tsunami. The original plan called for completing all decontamination by next March.

Nobody has been allowed to live in the zone again yet, though the government has allowed day visits to homes and businesses in some areas after initial decontamination efforts, said Shigeyoshi Sato, an Environment Ministry official in charge of decontamination.

"We would have to extend the cleanup process, by one year, two years or three years, we haven't exactly decided yet," he said.

Sato cited several reasons for the delay, including a lack of space to store the waste that comes out of the decontamination process. Some residents have opposed dumping the waste in their neighbourhoods.

The Asahi newspaper reported on Saturday that the government is planning an extension of up to three years in areas including Iitate, a village northwest of the plant where a highly radioactive plume spread in the first few days of the crisis.

An International Atomic Energy Agency team is also finishing a weeklong visit to check cleanup progress in Kawauchi, a less-contaminated community that has been partially opened to living again. So far, about 40 per cent of Kawauchi's population of 3,000 has returned to the village.

The government hopes to restore lost communities in some areas around the plant, but challenges remain in ensuring food safety and job security.