Hong Kong publisher Jimmy Lai entered house arrest this week after a judge ruled against prosecutors' attempt to see his HK$10 million ($1.3 million) bail overturned.

The 73-year old owner of anti-establishment newspaper Apple Daily returned home late Wednesday after spending 20 days in police custody for fraud charges and allegations of collusion under the National Security Law.

As the first person in Hong Kong to be granted bail for charges under the new law, he has been ordered to follow "tailor-made" conditions by Justice Alex Lee Wan-tang who also banned the business owner from engaging in acts "reasonably regarded as" hostile against China.

Also part of the agreement, Lai is forbidden from posting on social media, cannot leave Hong Kong and must report to the police three times a week.

The Apple Daily owner was taken into police custody Dec. 3 alongside Next Digital executives Royston Chow Tat-kuen, 63, and Wong Wai-keung, 59, for allegedly defrauding a government-owned business incubator where the newspaper rents offices.

Chow and Wong were later released after posting bail, while prosecutors charged Lai with the more serious charge of working with a foreign government - an offence punishable under the NSL with a maximum sentence of life imprisonment.

Lai "sits in jail for the sin of criticizing his government," American senator Marsha Blackburn, who is a noted hawk on China-related issues, wrote on Twitter after his arrest.

The case will be heard by the court in April and Lai will remain under house arrest until that time. The judge's decision to grant bail was appealed by prosecutor Anthony Chau Ting-hang, who requested the court "maintain the status quo" by keeping the accused in custody.

Justice Lee denied this appeal, noting he "did not have the jurisdiction" to weigh in on such matters.