TAIPEI (AFP) — Taiwan has stepped up national security measures, its premier said Tuesday, after a Chinese man was arrested for illegally entering the self-ruled island by boat.

Taiwan’s coast guard arrested the man on Sunday after his vessel collided with other boats on the Tamsui River, which flows from the capital Taipei to the island’s northern coast.

The man, 60, told coast guard officers at the scene that he wanted to “defect,” according to the semi-official Central News Agency.

The coast guard said his motive was under investigation and did not release his name or age.

“The government and all national security units and teams are paying close attention, and investigations have been launched on this case,” Premier Cho Jung-tai told reporters Tuesday.

“National security cannot be neglected for a minute,” he continued, adding that relevant units had been instructed to “immediately strengthen protective measures”.

China claims self-ruled democratic Taiwan as part of its territory, and it has ramped up military and political pressure on the island in recent years.

The Taiwan Strait — a 180-kilometer channel separating China from the island — is one of the world’s most heavily policed waterways.

Authorities did not say if the man had made his way from across the strait.

Taiwan is routinely on guard for spies from China.

The most recent prosecution was in April, when a father and son were both jailed for eight years for collecting confidential military information and trying to develop a spying “organization” for Beijing.

In the incident on Sunday, the coast guard said it first began monitoring the boat when it was spotted around 9 a.m. 11 kilometers off the coast of Tamsui, a district in the suburbs of Taipei.

The man was arrested “for further investigation into his method, channel, and purpose of coming to Taiwan,” the coast guard said in a statement Monday, urging the public to report “illegal activities” at sea or on the shore.

In 2021, a Chinese man was arrested in central Taichung city after he managed to cross the Taiwan Strait in a rubber dinghy.

He said he had come to Taiwan to seek “freedom and democracy,” according to police.