A former police officer accused of spying for communist China in one of the former British colony's highest-profile espionage cases has died, according to reports Tuesday.

Top Chinese leaders, including President Xi Jinping paid tribute to John Tsang Chao-ko, whose memorial service was held in the southern Chinese city of Guangzhou, after he died of an unspecified "illness" on December 18 at the age of 91, according to the state-run Guangzhou Daily.

Tsang, also known as "Hong Kong's first spy", was caught in a "shocking" arrest in the midst of the Cold War in 1961 under the "Deportation of Aliens Ordinance", Hong Kong newspapers reported.

A British special service unit arrested him after a tip-off from an agent Tsang worked with.

The agent was found at the border between Hong Kong and China carrying stacks of cash and microfilm, days before Tsang's arrest.

Hong Kong's Apple Daily newspaper said Tsang refused to consume drinks laced with drugs when he was detained in Hong Kong for around two months before he was deported to the mainland without a trial.

Before the arrest, he was then the city's most senior ethnic Chinese police officer and a deputy head to the local police training college. He had also just finished a training course at Cambridge University.

The colonial government alleged he was closely involved with a secret intelligence network in Hong Kong but his activities had never been confirmed by the Chinese government, the Hong Kong paper said.

After returning to China, Tsang became a member of the National People's Congress, the nation's rubber stamp parliament.

Guangzhou Daily described him as a "comrade" in an obituary but his past service in Hong Kong was not mentioned.