Prime Minister Shinzo Abe made the remarks in Ishigaki, an island about 150 kilometers (95 miles) southeast of the Japanese-controlled islands called Senkaku, which China also claims and calls Diaoyu. Abe is known for his hawkish security policy and nationalistic remarks, comments that have hurt Japan's relations with Asian neighbors.
"Today, we face a continuing provocation to our country's territorial land, sea and airspace," Abe said in an address to about 50 coast guard officers during his visit to Ishigaki, where he campaigned ahead of Sunday's parliamentary elections.
Abe said incursions by Chinese ships into the area around the disputed islands made "our country's territorial security environment an extremely challenging one." He urged the coast guard to boost their watchfulness.
Abe also took to the streets to make his campaign appeal to Ishigaki voters.
"Senkaku is undoubtedly Japan's inherent territory. Clearly, there is no territorial problem here. We will not make any compromise, not even a step, on this matter," he said.
Abe made a similar address Wednesday to soldiers stationed on Miyako island. Tougher territorial defense has been part of the campaign platform for Abe's ruling Liberal Democratic Party.
Japan nationalized the Senkaku in September to strengthen its territorial claims, leading to a diplomatic row between Tokyo and Beijing. Since then, official Chinese vessels have entered Japanese-claimed waters around the islands on 52 days, according to Japan's coast guard.
With the economy showing signs of improving under Abe's policies, his party is expected to win a comfortable majority in the upper house, allowing the governing coalition to regain control of both houses.