Travel companies say they are seeing slowing business between China and Japan as the two countries ratchet up the rhetoric in a territorial dispute over a group of East China Sea islands. That has led to occasionally violent protests in China with a definite anti-Japanese tone.

All Nippon Airways Co, Japan's biggest airline by passengers, said Tuesday that 18,800 seat reservations have been canceled on its routes between Japan and China for the period from September to November. Chinese budget carrier Spring Airlines Co. will cancel its 10 charter flights between Shanghai and the Japanese city of Tottori from Saturday to Nov. 25, a company spokesman said Tuesday.

China's largest online travel company, Shanghai-based Ctrip.com International Ltd CTRP -1.35%., says it is treating the political standoff like a natural disaster and allowing many travelers to get a full refund, which the company says has already led to cancellations of around half the group bookings reserved for the upcoming weeklong National Day holidays.

"Before, Japan was one of the most popular destinations for Ctrip," Tang Lan, the company's senior vice president, said in an interview Tuesday. "Unfortunately, a lot of customers called to cancel their trip."

Ctrip figures it has more than 40% of China's online travel business, and it estimates Japan represents as much as 20% of its international business.