Hong Kong democracy supporters flocked to buy copies of pro-democracy newspaper Apple Daily on Friday, citing anger over a police raid of its newsroom as part of an inquiry into whether some articles threatened China's national security.

The popular 26-year-old paper, which combines liberal discourse with celebrity gossip and investigations of those in power, increased its Friday press run to 500,000 copies, up from 80,000 the previous day.

Apple Daily's presses whirred out the first copies of the print run around midnight, and the papers were whisked away by vans and trucks across Hong Kong...