Hong Kong's largest national security case to date is set to resume on Wednesday lunchtime, with the bail hearing for 47 democracy campaigners going into a third day.

Several of the defendants have been taken to hospital since the case got underway at West Kowloon Magistrates' Court on Monday, and many of the others have been seen dozing off in the courtroom after being left with little time to sleep as they shuttled between court and jail.

Charges of conspiracy to commit subversion have been slapped on the former lawmakers and activists, in connection with the primary polls the pro-democracy camp held last summer to pick candidates for Legco elections which the government eventually cancelled.

During the hours of proceedings, lawyers for the 47 have been challenging a prosecution demand that bail be denied.

Chief Magistrate Victor So, one of those handpicked by Chief Executive Carrie Lam to hear national security cases, is to announce his decision for each defendant at the end of the proceedings.

The national security law which Beijing imposed on the territory last June overturns Hong Kong's presumption of bail for non-violent crimes and defendants have to offer evidence that they will not "continue" to commit acts endangering national security.

All of those charged under the legislation have so far been remanded in custody.