Officers wearing vests labelled "NSD", for National Security Department, led a woman in handcuffs to a van and took away several boxes of materials from the Have A Nice Stay bookshop.

Police and customs officers also searched the Greenfield Book Store, arresting three women and two men aged between 30 and 59, local media reported, citing unnamed sources.

They are suspected of selling publications with "seditious intention" under Hong Kong's national security law, broadcaster TVB reported, adding that the books had been shipped from overseas without giving further detail.

The homegrown security law was enacted in 2024 in addition to legislation imposed by Beijing after pro-democracy protests paralysed the financial hub in 2019.

The offence is punishable with up to seven years in prison.

Greenfield Book Store was closed when AFP reporters visited during opening hours.

AFP has reached out to police for comment.

- 'Difficult to keep going' -

The operation came a day after Have A Nice Stay said it would close in August, citing reasons including the social environment and its financial situation.

"Given the economic situation across Hong Kong as a whole, we can only pessimistically conclude that it will be very difficult to keep going," the bookstore said in a statement on Tuesday.

"The elusive 'red line' is, of course, another factor."

The raid is the third conducted on independent booksellers this year.

Officials in March arrested four employees from another bookstore, Book Punch, for selling "seditious" publications.

Two employees from Hunter bookstore were also arrested last month.

"The targeting and arrests of booksellers in Hong Kong expose what the Chinese government fears most: free thinking," said Yalkun Uluyol, China researcher at Human Rights Watch.

"Beijing is trying to impose a world where people think only what the authorities permit."

Have A Nice Stay bookshop was founded in 2022 by a group of former journalists under an increasingly constrained media environment.

Many of the books on sale focus on media literacy, democratic development and authoritarianism.

It also sells publications and merchandise produced by local media outlets and journalists.

"Civil society around a decade ago was very different... Now, having a space is precious because we don't have many groups and venues left," Sum Wan-wah, a veteran journalist who co-founded the shop, told AFP in 2023.