A Chinese father and son were picked up after arriving on a beach near Taipei on Friday, days before Taiwanese President Lai Ching-te celebrates his first year in office.

The pair had travelled undetected by motorised inflatable boat from China's Fujian province, the coast guard said.

"Such boats are not easily detected by radar and the personnel responsible for coastal patrol were patrolling other areas at the time," coast guard spokesman Hsieh Ching-chin told reporters.

"There is an urgent need to enhance patrol capabilities using technological support to prevent further undetected illegal entries," he said.

There had been five cases involving 38 individuals from China and Vietnam caught illegally entering Taiwan since January, the coast guard said.

Hsieh said the coast guard hoped to receive funding from a special budget for infrared thermal imaging equipment as well as drones and artificial intelligence warning systems "to effectively respond to China's increasingly severe grey-zone harassment", Hsieh said.

Infrared thermal imagers had been deployed on Kinmen, an outlying archipelago administered by Taiwan, and other places where "landings have happened before".

However, a round-the-clock coastal surveillance system "with no blind spots" would require "substantial funding", he said.

Beijing claims Taiwan as part of its territory and has threatened to use force to bring it under its control.

Taiwan accuses China of using "grey-zone" tactics -- actions that fall short of an act of war -- to weaken its defences.

Hsieh said more Chinese people were arriving illegally on Taiwan's main island than in the past and that it could be part of China's "cognitive warfare".

It was possible Beijing would "again use similar tactics" to "disrupt public morale" as Lai marks the first anniversary of his inauguration on Tuesday, Hsieh said.

China launched large-scale military drills around Taiwan after Lai took office last year.