Liu Caigui, director of the State Oceanic Administration, told a national maritime conference China will "take more responsibilities to steadfastly maintain the country's maritime rights and interests," Xinhua reported.
He said China would oppose any infringement of the country's territorial waters by Japan, Vietnam or the Philippines.
For the past four months, Chinese ships and planes have patrolled the waters off a chain of tiny islands claimed by China, Japan and Taiwan. China calls the islands Diaoyu; Japan calls them Senkaku.
In April 2012, Chinese surveillance vessels rescued fishermen being intimidated by a Filipino warship.
On Wednesday, Japan was reported planning to fire "warning shots" if it encountered Chinese surveillance planes over the islands.