SEOUL, South Korea — More than 100 South Korean schools have cancelled or shortened classes over fears that rain falling across the country may include radiation from Japan's stricken nuclear plant.

The Education Office of Gyeonggi province said it allowed schools to decide whether to open Thursday.

The prime minister's office said radiation levels in the rain were low and posed no health threat.

Still, officials said that 126 schools in Gyeonggi province, near the capital, Seoul, shut down and 43 others shortened class hours as a precaution.

The Ministry of Education, Science and Technology said only a few schools outside Gyeonggi cancelled classes Thursday.

Radiation levels fall quickly as you move away from the source, and officials have cleared the 12-mile (20-kilometre) radius around Japan's crippled Fukushima Dai-ichi nuclear complex.

Recent progress at the plant -- which was damaged by a March 11 tsunami -- appears to have slowed the release of radiation into the ocean. This week, technicians there plugged a crack that had been gushing contaminated water into the Pacific. Contamination in waters off the coast has fallen dramatically since then.