BEIJING (Reuters) - China's state prosecutor said on Monday it had formally charged Hong Kong actor-singer Jaycee Chan, son of movie star Jackie Chan, with a drugs offence, meaning he is almost certain to face trial.

The younger Chan, 32, was arrested in Beijing this year after testing positive for marijuana, with the police saying they found 100g of the drug at his home.

In a brief statement on its official microblog, the Supreme People's Procuratorate said it had begun legal proceedings against him for the crime of sheltering drug users. It did not elaborate. Previous reports said he could be jailed up to three years.

President Xi Jinping said in June that China would "harshly crack down" on narcotics, the state media reported.

Jackie Chan, 60, served as a goodwill spokesman for the China National Anti-Drug Committee in 2009, promoting anti-drug education. In August, he offered the public a "deep bow of apology" for his son's arrest.

Jaycee Chan was arrested with Taiwanese actor-singer Kai Ko, who has since been released but has been banned from show business in China. Ko, 23, made an unpaid appearance at a charity event in Taipei on Sunday. After the arrest, "I have fewer showbiz friends, I still go to the KTV", he said. But he has to report his activities to his agency, he added.