Justice Russell Coleman had granted on October 11 an interim injunction to put on hold an invalidation of the certificates, which were to have been nullified next day because of alleged failures by seven doctors who issued them.

The legal challenge came from retired civil servant Kwok Cheuk-kin, who said the Department of Health did not have the power to invalidate the certificates and asked the court to rule that Secretary for Health Lo Chung-mau exceeded his authority.

Kwok's lawyer, Hectar Pun Hei, had argued the prevention and control of disease ordinance did not grant Lo specific power to invalidate exemption certificates.

Even if Lo did have such power, Pun added, he had used it without going through proper procedures. Lo should have gone through the cases individually and verified the documents rather than invalidating them all.

Lo's counsel, Abraham Chan Lok-shung, countered that the invalidation statement should not be considered a legal document but an "instruction" to prevent potential public health risks because of questionable exemption certificates.

He added that Lo does have broad powers to make administrative decisions during a public health emergency, while it was impossible for Lo to review cases individually.

Speaking outside court, Kwok said he has "70 percent confidence" of winning, though it would be a "small win" for him.

The case, Kwok claimed, "has revealed the maladministration of the whole government."

He added: "How come the invalidation was approved without much discussion when many of the members in the Executive Council are legal professionals?"