Taipei’s defence ministry says 12 Chinese military aircraft and seven warships were detected until early Monday.

Taiwan’s defence ministry has reported that a Chinese balloon had been detected over the sea to the island’s northwest, the first time since April it has flagged such an incident.

The ministry reported on Monday that the latest balloon was spotted at 6:21pm (10:21 GMT) on Sunday about 111km (69 miles) northwest of Keelung City at an altitude of 33,000 feet (10,058 metres).

It entered the island’s air defence identification zone and disappeared at 8:15pm, according to the ministry, which releases daily data on China’s military presence around Taiwan.

As well as the balloon, 12 Chinese military aircraft and seven warships were detected around Taiwan in the 24 hours to early Monday, the ministry said.

China claims Taiwan as part of its territory and has repeatedly declared that it could forcefully stop Taipei in case it declares independence.

Beijing regularly deploys fighter jets, drones and warships around Taiwan, and occasionally balloons, as it keeps up military pressure.

Taiwan has described the balloons as a form of “grey zone” harassment – a tactic that falls short of an act of war.

In the weeks leading up to its presidential election in January, Taipei had also complained that Chinese balloon activity above the island’s territory was taking place at an “unprecedented scale”.

China’s defence ministry did not respond to a request for comment.

China has previously dismissed Taiwan’s complaints about the balloons, saying they were for meteorological purposes and should not be hyped up for political reasons.

The potential for China to use balloons for spying became a global issue last year when the United States shot down what it said was a Chinese surveillance balloon. China said the balloon was a civilian craft that accidentally drifted astray.

The latest balloon incident over Taiwan comes as Japan’s Kyodo news agency reported that the US is drawing up contingency plans for military deployments in Japan and the Philippines in case of an emergency over Taiwan.

They will be incorporated in a first joint operation plan to be formulated in December, the report said citing sources familiar with Japan-US relations.

A US Marine regiment which possesses the multiple-launch HIMARS (High Mobility Artillery Rocket System) would be deployed along Japan’s Nansei island chain stretching from Kyushu to Yonaguni near Taiwan, Kyodo said.

If a Taiwan contingency becomes highly imminent, temporary bases will also be set up on inhabited islands based on US military guidelines, the report added.

Japan’s military is expected to mainly engage in logistical support, it said.

The US Army would also deploy long-range fire units in the Philippines, Kyodo said.

Washington has been strengthening alliances in the region, infuriating Beijing.

Last year, the Philippines signed a defence pact with the US, giving its forces access to four more military bases in the Southeast Asian nation. Earlier this month, Manila and Washington signed a military intelligence-sharing deal, in a further deepening of security ties between the two defence treaty allies as they seek to counter a resurgent China.

Japan and the Philippines signed a defence pact in July, allowing the deployment of troops on each other’s soil.