TAIPEI, Oct 5 (Reuters) - Taiwan needs to be on alert for China's "over the top" military activities which are violating regional peace, Premier Su Tseng-chang said on Tuesday, after 56 Chinese aircraft flew into Taiwan's air defence zone on Monday, the highest ever.

Taiwan has reported 148 Chinese air force planes in the southern and southwestern part of its air defence zone over a four day period beginning on Friday, the same day China marked a key patriotic holiday, National Day.

China claims Taiwan as its own territory, which should be taken by force if necessary. Taiwan says they are an independent country and will defend their freedoms and democracy.

Taiwan calls China's repeated nearby military activities "grey zone" warfare, designed to both wear out Taiwan's forces by making them repeatedly scramble, and also to test Taiwan's responses.

"Taiwan must be on alert. China is more and more over the top," Su told reporters in Taipei. "The world has also seen China's repeated violations of regional peace and pressure on Taiwan."

Taiwan needs to "strengthen itself" and come together as one, he added.

"Only then will countries that want to annex Taiwan not dare to easily resort to force. Only when we help ourselves can others help us."

Taiwan President Tsai Ing-wen has made modernising the armed forces a priority, focusing on the use of new, mobile weapons to make any attack by China as costly as possible, turning Taiwan into a "porcupine".

The United States, Taiwan's main military supplier, has described China's increasing military activities near the island as destabilising and reiterated its "rock-solid" commitment to Taiwan.

In a sign of the fraught atmosphere, a security source confirmed reports in Taiwanese media that a Chinese pilot responded to a radio warning to fly away on Sunday with a shouted expletive.

China's Defence Ministry did not immediately respond to a request for comment.

Japan also weighed in on Tuesday, saying it was watching the situation closely and hoped Taiwan and China could resolve their differences through talks.

"Japan believes that it is crucial for the situation surrounding Taiwan to be peaceful and stable," Foreign Minister Toshimitsu Motegi said in Tokyo.

"Additionally, instead of simply monitoring the situation, we hope to weigh the various possible scenarios that may arise to consider what options we have, as well as the preparations we must make."

Taiwan has lived under the threat of invasion since the defeated Republic of China government fled to the island in 1949 after losing a civil war with the Communists. No peace treaty or armistice has ever been signed.

Taiwanese people are well used to China's threats and there has been no sign of panic on the island because of the stepped up military activity, nor undermining of investor confidence on the stock market.