China's recent decision to fire missiles over Taiwan is a "gorilla in the room" that has to be contested, a top US military commander said Tuesday.

Beijing has carried out huge air and sea drills this month around Taiwan in a furious reaction to visits by US House Speaker Nancy Pelosi and a congressional delegation.

Those exercises included firing multiple ballistic missiles into waters off Taiwan -- some of the world's busiest shipping routes -- and it was the first time China has taken such a step since the mid-1990s.

"It's very important that we contest this type of thing. I know that the gorilla in the room is launching missiles over Taiwan," Seventh Fleet Commander Vice Admiral Karl Thomas told reporters in Singapore.

"If we just allow that to happen, and we don't contest that, that'll be the next norm," he added.

"It's irresponsible to launch missiles over Taiwan into international waters, where the shipping lanes, where free shipping operates."

The Seventh Fleet is based in Japan and is a core part of Washington's navy presence in the Pacific.

During this month's drills Chinese state media reported that some of the ballistic missiles fired by the People's Liberation Army followed a trajectory directly over Taiwan's capital Taipei, a new escalation that Beijing stopped short of confirming.

Thomas compared the threats against Taiwan to the South China Sea where Beijing spent years constructing military bases and facilities on a series of contested atolls, while denying it was doing just that.

"If you don't challenge it... all of a sudden it can become just like the islands in the South China Sea (that) have now become military outposts," he said.

"They now are full functioning military outposts that have missiles on them, large runways, hangers, radars, listening posts."

China's communist party has never run Taiwan but it regards the island as its territory and has vowed to one day seize the island, by force if necessary.

Sabre rattling towards Taiwan have become more pronounced under Chinese President Xi Jinping.

The United States and other western allies have increased "freedom of navigation" crossings by naval vessels of both the Taiwan Strait and South China Sea to reinforce the concept that those seas are international waterways, sparking anger from Beijing.

China said it conducted new military drills on Monday as a delegation of US lawmakers visited Taipei.

State media ran footage and pictures of Taiwan's Penghu islands purportedly taken from Chinese jets flying a short distance from the archipelago.

But Taiwan denied that Chinese jets came close to Penghu.

"The CCP used cognitive warfare and other tricks to exaggerate and show that (its jet) was close to Penghu. This is not true," senior air force official Tung Pei-Lun told reporters on Tuesday.

The Penghu islands sit in between the Chinese mainland and Taiwan.

They host a major Taiwanese airbase and would be on the frontline of any invasion attempt by Beijing.