A Taiwanese news channel has broadcast by mistake a fictional news alert that said Chinese armed forces had launched an invasion, firing missiles at cities and ports surrounding the capital, Taipei.

Several news captions declaring a violent attack by China’s People’s Liberation Army had been mocked up for forthcoming security drills, but were broadcast accidentally to Taiwanese viewers at 7am on Wednesday.

“New Taipei City was hit by communist missiles, the Taipei port has exploded, facilities and ships were damaged and destroyed,” the Chinese Television Systems (CTS) news ticker read.

“On the brink of war … The Chinese Communist party prepares for war … The president has issued an emergency order.”

The partly government-owned CTS station issued an on-air “clarification and apology” several hours later, saying the report had been created in conjunction with emergency services for the drills, but had been accidentally broadcast.

“[Yesterday] CTS news channel cooperated with the New Taipei City government fire bureau to record a disaster prevention video. On the 20th, due to a wrong setting by the production staff, we mistakenly flashed the messages from yesterday about the war and disaster prevention. People do not need to panic.”

The New Taipei fire department told the Guardian the fake news alerts were supposed to be shown on 5 May during the annual disaster response drills, which will this year include a missile attack scenario.

“The exercise includes an earthquake scene, tsunami, a bridge collapse and explosion,” a spokesperson said. “This year, our boss said we will also include the war scenario in the exercise … It is the first time in recent years.”

Taiwan’s defence minister, Chiu Kuo-cheng, said he had been “surprised to see the news”. Chiu said the army had responded quickly to verify and dispel the erroneous alert. The error was “a good lesson to our journalist friends”, he said.

Screenshots of the broadcast spread across Taiwan’s social media, with some people expressing worry, some laughing at the error, and others criticising the TV station and media in general. “An unforgivable mistake, and perhaps not a mistake,” said one. “It needs serious punishment, they made social panic,” said another.

In China, the error was viewed or discussed by more than a million people on Weibo, under the hashtag: “Taiwan media makes a big own goal.”

Taiwanese opposition politicians called for regulators to punish the station for creating panic. Li Yong-de, the minister for culture who overseas public broadcasting, apologised. In a statement, CTS offered a “sincere apology that this serious flaw has caused panic among the public and trouble to relevant units”, and said those responsible would be punished.

Taiwan has lived under the threat of invasion by neighbouring China for decades. The ruling Communist party considers Taiwan to be a breakaway province of China, and has not ruled out using force to “unify” it. Taiwan rejects Beijing’s claim, saying it is already an independent nation.

Under the increasingly authoritarian rule of Xi Jinping, China’s government and armed forces have raised economic, diplomatic, and military pressure on Taiwan, including disinformation and propaganda campaigns. In the last two years there has been a marked increase of air force sorties into Taiwan’s air defence identification zone, and other military exercises designed to intimidate Taiwan, whose air force scrambles in response to each incursion.

Taiwan is considered to be at the highest risk of invasion than in several decades, and Russia’s invasion of Ukraine has sparked alarm among the island’s leaders and population, but few analysts or observers believe such an attack on Taiwan is imminent.