Apple Daily, a staunch anti-government and pro-democracy tabloid that also does investigative work, posted on its Facebook page a livestream of police officers roaming through its newsroom and rifling through files on Monday (August 10).
It also reported that Lai, an ardent critic of Beijing, had been taken from his home early on Monday.
The live feed showed staff being asked to show identity documents. Some executive offices were sealed off with red cordons. The police later wheeled in stacks of empty plastic containers.
Lai himself was brought back to the office later, initially in handcuffs.
Police said around 200 officers entered the premises with a court warrant. The law allows police to search premises without one "under exceptional circumstances," and also allows documents, equipment and financial assets to be seized.
The search was finished by mid-afternoon, and police said they had collected 25 boxes of evidence.
Lai became the highest-profile person arrested under a new national security law, detained over suspected collusion with foreign forces.