Hong Kong authorities say they have received confirmation from Chinese security officials that a bookseller whose disappearance three weeks ago raised international concern is in the mainland.

Hong Kong police said late Monday that they received notice from Guangdong province's public security department that Lee Bo was "understood" to be in mainland China.

Guangdong officials were replying to a request by Hong Kong police for information on Lee.

He and four other people linked to a Hong Kong publishing company and its bookshop had gone missing in recent months.

The publishing firm specialized in books banned in mainland China for being critical of its communist leadership.

Lee's case in particular raised alarm bells because it raised suspicions that Chinese security agents crossed into Hong Kong to abduct him.