China is preparing for a military invasion of Taiwan in 2020.

To counter the threat, Taipei has been conducting live-fire war drills.

The latest round of exercises will start next month.

Taiwan armed forces are planning a three-day live-fire military exercise on Taiping Island in the heavily disputed waters of the South China Sea to show claim to its sovereignty over the Spratly Islands -- a move that will anger China and maybe Vietnam.

According to the South China Morning Post, the exercise is scheduled between 8 am and 9 am from November 21 to 23, is expected to upset Beijing, which has also claimed the Spratlys.

"Beijing's sovereignty claim over the Spratlys is consistent with that of Taipei's, and any live-fire drills on Taiping only serve to reinforce the mainland's sovereignty over the region, given that Beijing considers Taiwan a part of China," said Wang Kung-yi a professor of political science at Chinese Culture University in Taipei.

Taiwan's Coast Guard Administration said Tuesday that the drill would involve firing into the sea and air in the area around Taiping Islands -- using 40mm grenade machine guns and other heavy weapons.

"It is a routine shooting practice, which we have held for years," Tsai Tzung-hsien, head of the public relations department of the coastguard, told the South China Morning Post.

The drill will be held within a five nautical mile range of Taiping, is aimed at safeguarding the integrity of Taiwan's territory and thwarting an invasion from Beijing.

Tsai said the drill would not endanger commercial shipping lanes close to Taiping.

South China Morning Post asked what sorts of weapons would be used, Tsai said: "We will test the responsiveness both our light and heavy weapons as well as our personnel."

The South China Sea is a heavily disputed economic zone and has overlapping maritime claims by Brunei, China, Taiwan, Malaysia, Indonesia, the Philippines, and Vietnam. An estimated $5 trillion of global trade flows through the region annually, which the U.S. and Australia want shipping channels to remain international waters and have launched "freedom of navigation" operations in the region.

Two US Navy destroyers sailed through the Taiwan Strait on Monday, in a move to aggravate China amid heightened trade war tensions with Beijing.

The USS Curtis Wilbur and USS Antietam, both Arleigh Burke-class destroyers, conducted routine transit to show U.S. commitment "to free and open Indo-Pacific," said Colonel Rob Manning on Monday.

This was the third "freedom of navigation" operation by American destroyers in the second half of this year. Multiple Chinese warships followed the two US ships during the transit, defense officials told CNN.

It seems Taiwan has good reason to prepare for a Chinese invasion.

Geopolitical intelligence analyst, in a separate report, told the South China Morning Post that Beijing's effort to increase military readiness and defend the "one China" policy, was uncovered in a leaked document specifying Beijing has a secret plan to invade Taiwan by 2020.