The two sides have been spying on each other for decades, but analysts say the threat to Taiwan is greater given that China has threatened to use force to bring Taipei under its control.

Taipei District Court convicted nine defendants of violating the National Security Act for "developing an organisation for China", while another was found guilty of illegal currency exchange.

The ringleader Lu Chi-hsien was a coach for "diabolo" -- Chinese yo-yo -- who was recruited during a visit to China, prosecutors said in November when he was indicted.

Lu was "persuaded and enticed" by a Chinese "intelligence agent" and was paid to "develop an organisation, collect intelligence and military data", the court said in a statement.

Lu recruited five former or then-active military and coast guard personnel, who went on to convince a dozen others to join them and hand over military documents.

The ringleader was paid by Tian Xi, the only Chinese national among the defendants, who handled around NT$194 million ($6.6 million).

He was given an eight-year prison term, while Lu was jailed for 10 years and six months, and the others were sentenced to between three and six years. They can appeal the ruling.

Aside from the five recruited from the military and coast guard, those convicted included three friends of Lu, who moved a safe house, provided bank accounts, and digitised and delivered military documents to him.

The number of people prosecuted for spying for Beijing has risen sharply in recent years, with retired and serving members of Taiwan's military the main targets of Chinese infiltration efforts, official figures show.