China is trying to set a "red line" for the incoming Trump administration and U.S. allies by stepping up military activities in the region, a senior Taiwan security official said, including likely war games this weekend around the island.

China, which claims democratically governed Taiwan as its own territory over Taipei's rejection, has held two rounds of war games around the island so far this year, and its forces operate nearby on a daily basis.

The official confirmed concerns expressed by other security officials in the region who have previously told Reuters that China could launch new drills to coincide with Taiwan President Lai Ching-te's trip to the Pacific this week which included visits to Hawaii and the U.S. territory of Guam.

"They want to clearly establish that the First Island Chain is China's red line and its sphere of control before the new U.S. government takes office on Jan. 20," the official told a briefing in Taipei, offering the government's assessment of China's activities.

The First Island Chain is an area that runs from Japan through Taiwan, the Philippines and on to Borneo, enclosing China's coastal seas.

Neither China's Taiwan Affairs Office nor its defence ministry responded to a request for comment.

The Taiwan official, briefing on condition of anonymity to be able to speak more freely, said China could launch new war games shortly before or after Lai's return to Taipei from the Pacific on Friday.

"They want to tell the new U.S. government that this area is controlled by China and that you must discuss with China everything that happens here," the official said, pointing to recent Chinese military activities around Taiwan including joint manoeuvres with Russia near the island's east coast earlier this week.

"They want other countries - the United States or Europe - to know that this is their sphere of influence and that they should be taken seriously."

China has deployed close to 40 vessels in the region this week, including a Chinese aircraft carrier group led by Liaoning in the East China Sea as well as other naval and coastguard boats in the South China Sea.

Reuters first reported that a north bound Russian naval fleet on Monday approached close to Taiwan's contiguous zone 24 nautical miles (45 km) off its southeastern coasts and conducted joint simulated attacks on "foreign vessels and aircraft" with a Chinese destroyer nearby.

China urged the United States last week to exercise the "utmost caution" on relations with Taiwan, ahead of Lai's Pacific tour. Beijing opposes any foreign interactions or visits by Taiwan leaders.

Lai and his government reject Beijing's sovereignty claims, saying only the island's people can decide their future.