Thousands of protesters in Hong Kong have taken to the streets to demand answers over the disappearance of a book editor and four of his colleagues.

Sunday's march was the largest since the publishers, linked to a shop selling political books critical of China's communist party leaders, began to go missing two months ago.

The last of the five men, Lee Bo, was last seen in Hong Kong on December 30. At the time of his disappearance, Lee was the chief editor of Mighty Current, which sells books banned in the mainland.

Publisher goes missing in Hong Kong

Mighty Current and its Causeway Bay Bookstore are known for titles about Chinese political scandals and other sensitive issues popular with visiting tourists from the mainland.

Beijing has yet to officially confirm that the five men are being held.

But Lee has reportedly called his wife to tell her that he is assisting Chinese authorities with an investigation - and that they should not make a scene about his disappearance.

The case has raised fears that China is undermining Hong Kong's press freedom.

Al Jazeera's Rob McBride, reporting from the protest scene in Hong Kong, said that "several thousands" had taken part in Sunday's event, with organisers estimating that up to 6,000 demonstrators were in attendance.

"Many here regard this [case] as the latest evidence on [Hong Kong's] semi-autonomous status being undermined," McBride said.

In addition to the threats they feel the case poses to press freedoms, protesters also consider this case an attack on judicial independence, he added.

The possibility of Lee being abducted from Hong Kong and smuggled across the border "really scares people here", he said.

Source: Al Jazeera