Hong Kong’s national security police have arrested a man on suspicion of being involved in terrorist plots, including plans to bomb infrastructure and courts, as well as set fire to a government Covid-19 test centre.

Police on Tuesday said the 22-year-old suspect arrested in Yuen Long the night before was believed to have connections with several criminal groups, with an insider indicating these included the now-defunct pro-independence Returning Valiant and radical anti-government body Black Bloc.

Fourteen members of Returning Valiant were arrested in July last year and seven have been charged in connection with an alleged terrorist plot. They had allegedly planned to make bombs and launch attacks against public facilities such as tunnels, railways and courts, according to a police spokesman.

The suspect was accused of supporting Returning Valiant, including through financial assistance, and taking part in an arson attack on a government Covid-19 testing station on Sha Tsui Road in Tsuen Wan on May 28 last year as a member of Black Bloc, the insider said.

He and two others, a 20-year-old man and a 52-year-old woman, are also thought to have been involved in planning a repeat arson attack on the same Covid-19 testing station this year.

They were arrested on Monday in North Point and Kowloon City on suspicion of conspiracy to commit arson.

Additionally, the 22-year-old allegedly conspired with four others to cheat a bank out of HK$4.7 million (US$598,740) by misusing a government small to medium enterprise financing guarantee scheme expanded last year to ease the economic difficulties that companies faced because of the Covid-19 pandemic.

Two other men and two women, aged 36 to 43, were arrested for conspiracy to defraud and money laundering on Tuesday morning in connection with the loan case.