Activists were barred Wednesday from leaving Hong Kong waters on what they called a "fishing" boat trip to disputed islands, more than a year after sailing to another contested chain to assert China's sovereignty.

"The Marine Department and police forcefully towed the boat to a police facility," a statement from the group said late Wednesday.

Police could not immediately comment.

The 13-strong group had planned to make what it termed a fishing trip to the Spratly Islands, but did not rule out sailing to other Chinese-administered areas.

The Spratlys in the South China Sea are disputed between Taiwan, Brunei, China, Malaysia, the Philippines and Vietnam.

In August last year the same group of nationalist activists used the fishing boat to land on disputed islands in the East China Sea known as the Senkakus in Japan and as the Diaoyus in China.

They planted a Chinese flag but were arrested and deported by Japanese authorities, who control the islands.

Officials in Hong Kong, a semi-autonomous southern Chinese city, have several times tried to thwart trips by the group, prompting speculation that Beijing does not favour such high-profile protests.

On Wednesday the activists' departure from Hong Kong's Victoria Harbour was delayed by several checks on their vessel, the Kai Fung No. 2.

On one occasion police boarded the boat and prevented it from setting sail for nearly an hour.

When the boat finally set off from the harbour in the afternoon, it was followed by several government vessels

The group in August this year had tried to repeat its journey to the Diaoyus. But Hong Kong's Marine Department stopped the 150-foot (45-metre) vessel from setting sail for "safety reasons".