The United States sent two long-range bombers into China’s air defence identification zone (ADIZ) on Tuesday in an apparent show of force, as the Chinese navy conducted a series of simultaneous massive drills.

According to aviation tracker Aircraft Spots, two US Air Force B-1B Lancer bombers left Andersen Air Force Base in Guam on Tuesday morning and entered China’s ADIZ over the East China Sea.

Aircraft Spots said the bombers were refeulled in flight during the mission.

The B1-B has the biggest payload of any bomber and is a departure from the fighter jets and spy planes the American forces have sent before on missions so close to the Chinese coast.

Such heavy aircraft are not known for being deployed on spying missions, suggesting that the US was sending a blunt warning.

The US bomber mission comes amid uncertainty in the US, where US President Donald Trump has refused to concede defeat to challenger Joe Biden two weeks after the presidential election.

The uncertainty has raised concerns in Beijing about the possibility of an accidental conflict.

Aircraft Spots said the US bombers flew very close to the northeast corner of Taiwan’s ADIZ and they would have entered the zone if they had continued on the same trajectory.

Under international rules, aircraft flying over such zones should notify the relevant authorities before doing so.

But the US and Japan do not recognise China’s claims over the area.

Also on Tuesday, a Taiwan air force F-16 disappeared off the coast of Hualien during an evening mission.

Military authorities said they were investigating the case and it was not clear if it was related to any military drills in the area.

The bombers’ mission also coincided with Chinese naval drills conducted simultaneously in the South China Sea, East China Sea and Bohai Sea.

Military analysts said the exercises were a signal from China’s top brass that the People’s Liberation Army could conduct joint operations in different military theatres at the same time.

The PLA drills were announced indirectly by China’s Maritime Safety Administration, which issued notices warning vessels to stay away from an area from the southern tip of the Yellow Sea to waters near Hainan Island. The no-go zone included an area with a 5km (3 mile) radius off the coast of Beihai in the southwestern region of Guangxi.

Another area in the South China Sea, in Honghai Bay southwest of Shanwei in southern Guangdong province, was restricted to traffic from Tuesday morning to early evening for “military training”.

Honghai Bay is about 100km (62 miles) from Taiwan-controlled Pratas Island, which is also claimed by Beijing.

Hong Kong-based military commentator Song Zhongping said the naval exercises would probably involve rocket launches.

“The 5km [3-mile] radius [of the restricted areas] indicates that the strikes are to test their high precision [ability],” said Song, a former instructor in the PLA Second Artillery Corps, the predecessor of the Rocket Force.

Song said the exercises indicated the PLA could mobilise forces in different regions in an emergency.

“Unexpected military clashes can happen anywhere, and if conflict happens in the Taiwan Strait, it could quickly turn out to be a large-scale military confrontation, and the Chinese military needs the ability to counterattack in the worst scenario,” he said.

John Bradford, a senior fellow specialising in maritime security issues at the S. Rajaratnam School of International Studies at Singapore’s Nanyang Technological University, said that by holding four exercises at the same time, the Chinese navy was clearly showing its military readiness.

“Such demonstrations will become more regular as the PLA Navy continues to expand the size of its force and the range of its operational competencies … In fact, we should expect this sort of thing to happen more frequently as the Chinese navy grows in size and mission,” Bradford said.

Collin Koh, a research fellow also from the S Rajaratnam School of International Studies, said the drills were in response to what Beijing saw as an increasingly complex security environment.

“What I’ll see as something to watch is how these drills integrate various agencies, such as the PLA, civilian bodies and so on. This would be a logical expectation after the Central Military Commission recently issued a new outline on promoting joint operations in the PLA,” said Koh, referring to the body that commands and controls the military.

China’s defence ministry did not respond to requests for comment on Tuesday.