The "yellow rain" seen Wednesday in the Kanto region surrounding Tokyo was caused by pollen, not radioactive materials as many residents feared, the Meteorological Agency said Thursday.

The agency received more than 200 inquiries Thursday morning about yellowish residue left on roofs and elsewhere by the rain, stirring concerns that radioactive substances had fallen in the wake of explosions at the Fukushima No. 1 nuclear power plant, around 220 km northeast of central Tokyo.

According to the Environment Ministry, large amounts of air-borne pollen were seen in the Kanto region and the pollen fell with the rain Wednesday.