China Southern Airlines, one of the three major Chinese airlines, on Tuesday announced it is cutting flights to the Philippines as tourist numbers shrink amid tensions in the South China Sea.

China Southern will reduce its number of flights between China's Guangzhou city and Manila, capital of the Philippines, to just one a day on certain dates from May 26 to June 30. The airline normally operates two flights daily on the route.

A spokesman for the airline said the adjustment was made in accordance with the cancellation of "a large number of tourist groups" lately.

Major Chinese travel agencies have announced cancellation of package tours to the Philippines upon travel safety advice issued by the National Tourism Administration earlier this month. It came after the Chinese Embassy in the Philippines warned Chinese citizens of "massive anti-China demonstrations" related to the Huangyan Island incident.

The tourism administration on Sunday said almost all Chinese mainlanders on group tours will leave the Philippines by Wednesday.

Major airlines serving the Chinese mainland and cities in the Philippines include Air China, China Southern, Philippine Airlines and Cebu Pacific Air.

Tensions in the South China Sea started on April 10, when a Philippine warship harassed 12 Chinese fishing vessels that had sailed near the island to seek shelter from inclement weather.

Chinese officials have repeatedly stated that Huangyan Island is an inherent part of China's territory and that the surrounding waters are historic fishing areas for Chinese fishermen.

Foreign Ministry spokesman Hong Lei on Monday urged the Philippines to respect China's territorial sovereignty and "refrain from taking action that could expand and complicate the situation."