Eight Chinese government ships entered Japanese territorial waters near disputed islands on Tuesday, the most in a single day since Tokyo nationalised part of the archipelago, the Japanese government said.
Japan's coastguard confirmed the vessels had entered waters near the East China Sea island chain, while the government's top spokesman said the flotilla was a one-day record since Tokyo's nationalisation in September.
The maritime surveillance ships entered the 12-nautical-mile zone off the Senkaku chain of islands, which China calls the Diaoyu, around 8:00 am (2300 GMT yesterday), the Japan Coast Guard said in a statement.
State-owned Chinese ships have frequently spent time around the five disputed islands, also claimed by Taiwan, in recent months.
"It is extremely deplorable and unacceptable that Chinese government ships are repeatedly entering Japanese territorial waters. We have made a firm protest against China both in Beijing and Tokyo," Japan's chief cabinet secretary Yoshihide Suga told reporters.
Meanwhile, a group of Japanese nationalists said it had sent nine ships to the area around the islands.