Vast amounts of pumice pebbles, spewed out months ago by an undersea volcano, has clogged dozens of ports and damaged fishing boats along Japan’s southernmost coastlines.

Deputy chief cabinet secretary Yoshihiko Isozaki said on Friday that the pumice had so far affected 11 ports on Okinawa and 19 others in the Kagoshima prefecture, on Japan’s southernmost island of Kyushu, and forced the central government to establish a disaster recovery task force.

About 40 fishing boats have been damaged, including six that were unable to move, and ferry services connecting remote islands in Okinawa and Kagoshima have been temporarily suspended.

Okinawa Governor Denny Tamaki said there had been a “huge impact on the fisheries and tourism industries as well as the environment” and that the problem must be tackled quickly.

The clean-up operation has begun – in one port in the village of Kunigami on the northern tip of Okinawa’s main island, about about 10 tonnes of pumice were reportedly being removed every day by huge diggers, with more washing ashore. One prefectural government official was quoted as saying the “unprecedented” operation could take two to three weeks to complete.

“We have no choice but to proceed with the cleanup work by trial and error,” Kyodo News quoted the official as saying. “We will think about how to dispose of the pumice stones after checking safety aspects.”

The grey pebbles came from the Fukutokuokanoba undersea volcano, hundreds of kilometres away in the Ogasawara island chain, which erupted in mid-August. The islands lie about 1,000km (600 miles) south of Tokyo.

The Japanese Coast Guard distributed a map showing the drift pattern of the pumice and warned vessels in the area to keep a close eye to avoid their engine systems becoming clogged by the pebbles. One of its own patrol vessels became stranded during training exercises on Saturday after encountering the pebbles off the coast of Okinawa.

Isozaki warned that the pebbles were moving north and could affect entire Japanese coasts. “Seeing as the pumice on the sea surface could spread to a wide area of Japan, we will continue to deal with the matter carefully,” he said.

The government task force, at its first meeting late on Thursday, decided to provide support for local municipalities as a disaster recovery project, and that the damage to fishing industries will be covered by insurance, Isozaki said. The total cost of the disaster is still unknown.

The Yomiuri Shimbun reported that about 750 fishing boats had been unable to leave port in Okinawa due to concerns about engine trouble, and that about 150 Indian mackerel, which were being farmed locally, died after apparently swallowing pumice.

The Nuclear Regulation Authority also watches the pebble movements to avoid any impact on Japan’s coastal nuclear power plants.

With Associated Press