Genetically modified rapeseed is proliferating around ports in Chiba, Yokohama, Nagoya and Kobe, after its propagation was confirmed in other places such as Kashima port in Ibaraki Prefecture and Yokkaichi port in Mie Prefecture, activist groups said Saturday.

The spread of the rapeseed may damage conventional rapeseed and other agricultural products, said the groups, including Stop GM Seeds Network Japan.

They said they believe imported genetically modified rapeseed has dropped out of containers during unloading or transporting and has taken root.

Japan imports some 2 million tons of rapeseed annually, mainly as an ingredient for cooking oil.