Hong Kong's Apple Daily has responded with defiance to the arrest of its owner under a new national security law imposed by Beijing, promising to "fight on" in a front-page headline over an image of Jimmy Lai in handcuffs.

Readers queued from the early hours of Tuesday to get copies of the pro-democracy newspaper, a day after police raided its offices and took Lai into detention, the highest-profile arrest so far under the new national security law.

More than 500,000 copies were printed, up from the usual 100,000, the newspaper said on its website.

"Yesterday will not be the darkest day for Apple Daily as the subsequent nuisances, suppression and arrests will continue to induce fear in us," it wrote in an editorial.

"Nevertheless, the prayers and encouragement of many readers and writers make us believe that as long as there are readers, there will be writers, and that Apple Daily shall certainly fight on."