China's military said it carried out more exercises near Taiwan today as a group of US lawmakers visited the Chinese-claimed island and met President Tsai Ing-wen, who said her government was committed to maintaining stability.

The five US lawmakers, led by Senator Ed Markey, arrived in Taipei on an unannounced visit late yesterday, the second high-level group to visit following that of US Speaker Nancy Pelosi early this month which set off several days of Chinese war games.

The Chinese military unit responsible for the area adjacent to Taiwan, the People's Liberation Army's Eastern Theatre Command, said it had organised multi-service joint combat readiness patrols and combat drills in the sea and airspace around Taiwan todau.

The exercises were "a stern deterrent to the US and Taiwan continuing to play political tricks and undermine peace and stability across the Taiwan Strait", it added.

China's Defence Ministry said in a separate statement that the lawmakers' trip infringed on China's sovereignty and territorial integrity and "fully exposes the true face of the US as a spoiler and spoiler of peace and stability in the Taiwan Strait".

"The Chinese People's Liberation Army continues to train and prepare for war, resolutely defends national sovereignty and territorial integrity and will resolutely crush any form of 'Taiwan independence' separatism and foreign interference."

The theatre command said the exercises took place near Taiwan's Penghu islands, which are in the Taiwan Strait and are home to a major air base and showed close-up video of the islands taken by a Chinese air force aircraft.

Tsai, meeting the lawmakers in her office, said China's exercises had greatly affected regional peace and stability.

"We are engaging in close cooperation with international allies to closely monitor the military situation. At the same time we are doing everything we can to let the world know that Taiwan is determined to safeguard stability and the status quo in the Taiwan Strait," she said, in video footage provided by the presidential office.

Markey told Tsai that "we have a moral obligation" to do everything to prevent an unnecessary conflict.

"Taiwan has demonstrated incredible restraint and discretion during challenging times," he added.

Low-key visit

Pelosi's visit infuriated China, which responded with test launches of ballistic missiles over Taipei for the first time and ditched some lines of dialogue with Washington, including theatre military talks and on climate change.

However, this trip was much more low-key than Pelosi's, with Tsai's meeting with the lawmakers not carried live on her social media pages, which is the general practice when high-level foreign guests come.

The group left Taiwan late today afternoon, and only after then did the presidential office release footage of the meeting with Tsai.

It was not immediately clear where they were going.

The de facto US embassy in Taipei said they had also met Foreign Minister Joseph Wu and members of Taiwan's parliament's foreign affairs and defence committee.

"Authoritarian China can't dictate how democratic Taiwan makes friends," Wu said on Twitter of their meeting.

The US has no formal diplomatic ties with Taiwan but is bound by law to provide the democratically governed island with the means to defend itself.

China has never ruled out using force to bring Taiwan under its control. Taiwan's government says the People's Republic of China has never ruled the island and so has no right to claim it, and that only its 23 million people can decide their future.

Taiwan Premier Su Tseng-chang said they would not be deterred by China's response to such visits by foreign friends.

"We can't just do nothing because there is an evil neighbour next door and not dare to let visitors or friends come," he told reporters.

- Reuters