Hundreds of people have protested in Hong Kong against a veteran newspaper editor's dismissal that has increased concerns about press freedom in the semi-autonomous Chinese territory.

The sacking of Keung Kwok-yuen, Ming Pao daily's second-in-command editor, came after the newspaper published a report on the Panama Papers document leak revealing offshore business dealings of the rich and powerful.

The newspaper said Keung was dismissed to save operating costs.

Journalists, activists and politicians attended Monday's rally, held outside the Ming Pao Industrial Centre.

READ MORE: Panama Papers - huge leak alleges elites hiding money

Protesters carried signs saying "Protect journalists, protect Ming Pao, protect press freedom".

Al Jazeera's Sarah Clarke, reporting from the protest, said: "The anger is not only confined to this particular newspaper but is spread around the whole news industry in Hong Kong.

"Some say that the city's press freedoms have been steeply eroded by the increasing influence from mainland China."

Rich and powerful

The trove of documents, released in April by the International Consortium of Investigative Journalists, has exposed how Mossack Fonseca, a Panama-based law firm, helped China's rich and powerful to move their wealth into tax havens.

"The public is very concerned over press freedoms in Hong Kong. We have been doing a good job... covering a lot of news including sensitive political issues such as human rights in China," AFP news agency quoted Phyllis Tsang, head of the newspaper's staff association, as saying.

"We demand a clear explanation [from the management] on the real reasons for the firing of Mr Keung.

"Was there any relation to this kind of reporting?"

Before Keung's dismissal, Ming Pao carried a front-page report on Hong Kong politicians and businesspeople named in the Panama Papers.

There has been growing anxiety in recent years among many Hong Kong journalists and politicians about the influence of China on the territory.

Hong Kong retained its own civil liberties when it was handed over from Britain in 1997.

Media groups with close business and personal ties to Chinese politicians have been accused of soft-pedalling their coverage of issues that are potentially embarrassing to China and its allies in Hong Kong.