Taipei: China once again showed its assertiveness toward Taiwan when its 30 warplanes made incursions into the island nation's air defence identification zone, or ADIZ on Monday, while US congressional delegation was on a surprise visit to Taiwan.

A US delegation led by Sen Tammy Duckworth, an Illinois Democrat, arrived in Taipei on Monday in a previously unannounced visit, Taiwan's Foreign Ministry said, reported CNN.

Taiwan's Ministry of National Defence said 30 Chinese warplanes made incursions into its air defence identification zone, or ADIZ, the highest daily figure in more than four months.

In response, the Taiwanese military issued radio warnings and deployed air defence missile systems to monitor the activities, the ministry added.

The delegation will meet with Taiwan's President Tsai Ing-wen on Tuesday, where they will discuss "regional security, economic and trade cooperation, and all issues related to US-Taiwan bilateral relations," presidential spokesperson Xavier Chang said.

During their visit, the delegation will also meet Premier Su Tseng-chang and Economic Affairs Minister Wang Mei-hua, before departing on Wednesday, reported CNN.

The visit comes after President Joe Biden recently took his first presidential trip to Asia -- and reignited a conversation over the US diplomatic posture toward Taiwan and mainland China.

Earlier this month, during a news conference in Tokyo, Biden said that the US would intervene militarily if China attempts to take Taiwan by force.

The warning appeared to deviate from the deliberate ambiguity traditionally held by Washington, though the White House quickly downplayed the comments, saying they don't reflect a change in US policy, reported CNN.

Under the "One China" policy, the US acknowledges China's position that Taiwan is part of China, but has never officially recognized Beijing's claim to the self-governing island of 23 million.

The US provides Taiwan defensive weapons, but has remained intentionally ambiguous on whether it would intervene militarily in the event of a Chinese attack.

China responded to the President's strong warning by expressing "strong dissatisfaction and firm opposition" to Biden's comments, saying it will not allow any external force to interfere in its "internal affairs," reported CNN.

Biden's warning made headlines around the world -- and put growing tensions between the small democratic island and its neighbouring autocratic superpower back in the spotlight.

Meanwhile, Taiwan was excluded from the Indo-Pacific Economic Framework, a regional economic plan recently unveiled by Biden during his Asia trip. The framework is Biden's attempt at engaging a region increasingly coming under the influence of China.

But Taiwan and the US could begin talks to deepen trade and economic ties "in a few weeks," two senior Taiwanese government officials have told CNN.