A Japanese coast guard vessel releases black smoke at a boat carrying Taiwanese activists attempting to reach disputed islands in the South China Sea.

Tension over the islands, known as Senkaku in Japan, Diaoyu in China and Diaoyutai in Taiwan have soared in recent months.

A fishing boat with four activists on board left Taiwan early on Thursday morning, escorted by Taiwanese coast guards.

One of the vessels displayed a sign which stated Taiwan's territorial claim.

The Japanese coast guards met the boats when they were 32 kilometres from the disputed islands, and turned them back.