Japan's infrastructure ministry has asked experts to study effective ways to remove pumice stones that are clogging cargo shipping ports.
Large volumes of the lightweight stones were ejected by an undersea volcano that erupted in August in the Pacific, near the Ogasawara Islands.
Since mid-October, the stones have reached coastlines, including fishing and shipping ports, in Okinawa and Kagoshima prefectures in southwestern Japan.
Aerial footage shot by NHK on Friday shows what appear to be pumice stones also drifting about 200 kilometers off Kochi Prefecture in western Japan.
Ministry officials who oversee cargo-handling ports met experts from maritime civil engineering firms and research institutions on Friday.
A senior official said that preparations must be made for extensive recovery work, as the stones could spread further east to Japan's main island of Honshu.
Work to collect the stones has been hampered by a lack of customized equipment.
Participants were told that pumping up seawater proved less effective than using backhoes and nets to remove the pumice.
The ministry plans to draw up a report on possible collection methods this month and share the results with coastal municipalities.