People’s Liberation Army fighter jets approached the southwest of Taiwan on Wednesday, according to its defence ministry, soon after the self-ruled island began a series of missile tests. Multiple Su-30 and J-10 fighter jets briefly entered Taiwan’s southwest air defence identification zone (ADIZ) before they were chased off by Taiwanese warplanes, the island’s defence ministry said in a statement. It said the PLA fighter jets had “entered the ‘response area’ of the southwest side of our ADIZ” in the morning, meaning the island’s military was required to respond to the situation. “What the Chinese communists did not only unilaterally, but also seriously, violated peace and stability in the region. For this we gravely condemn their acts,” the ministry said. It said Taiwan’s air force had closely monitored the PLA jets and drove them out of the ADIZ, adding that the Taiwanese public should rest assured that the military was able to respond to such incidents and safeguard the island. Beijing sees Taiwan as part of its territory and has not ruled out the use of force to bring the island under its control. Relations across the strait have deteriorated under Taiwanese President Tsai Ing-wen’s independence-leaning administration, and the PLA has stepped up military activities nearby as part of efforts to put pressure on the island. China plans sanctions against US officials who visit Taiwan, says Global Times editor Hu Xijin The PLA jets approached the southwest area at least 24 times between 7.07am and 9.30am, according to Taipei-based newspaper Liberty Times , citing a plane-watcher. It said Taiwan’s air force had sent jets to shadow the mainland Chinese aircraft and warned them to leave over the radio. The report said the PLA jets had entered the ADIZ at altitudes ranging from 1,500 metres (4,920ft) to 9,000 metres (29,530ft). It came after an unspecified number of missile tests were carried out between 5am and 7am on Wednesday by Taiwan’s state-funded National Chung-shan Institute of Science and Technology. More weapons tests – conducted off the island’s southern, eastern and northeastern coasts – are expected on Thursday, according to a notice from the institute. It said authorities including the transport ministry and fisheries agency had approved the tests to be conducted between Tuesday and September 17. It was not clear what types of weapons were being test-fired since their altitude was described as “limitless” in the notice, but local military experts said they could have included surface-to-air missiles, long-range supersonic cruise missiles and anti-ship cruise missiles – all of which have long ranges. The institute declined to comment or give further details of the missile tests. Taiwanese media reports speculated that the PLA warplanes were seeking to gather intelligence on the weapons tests, but defence expert Chieh Chung believed it was more a show of strength. “From what the defence ministry indicated, the PLA jets, which included Su-30s and J-10s, were practising formation warfare,” said Chieh, a senior national security researcher at the National Policy Foundation, a think tank in Taipei. “What was special this time was that the planes approached the ‘response area’ where our air force jets were standing by, meaning our air force was ready to take action if the PLA planes continued their incursions.” Fighter jets cross a line in Taiwan Strait, says Taipei as it hosts US health official amid rising US-China tension He noted that the warplanes had come closer than before to Taiwan’s outlying Penghu archipelago. “This also looks like the PLA was trying to demonstrate its striking ability,” Chieh said. He added that it was also likely the PLA had surveillance planes and ships observing the missile tests.