Reporters Without Borders (RSF) is calling for the immediate and unconditional release of a Pakistani journalist who it says has been held for days on a "flimsy" charge of posting "anti-state" content on social media.

Police in the city of Lahore arrested Azhar-ul Haq Wahid on January 16, and a local judge on January 20 rejected a request for his release, ordering him placed in judicial custody, RSF said in a statement.

The Paris-based media-freedom watchdog said Wahid, a reporter for Channel 5 TV and the newspaper Khabrain, is facing up to three years in prison.

His arrest "is clearly another attempt to intimidate journalists who refuse to be censored," said Daniel Bastard, the head of RSF's Asia-Pacific desk.

"We call on the Lahore courts to dismiss the charges against him and to free him at once. The credibility of the rule of law in Pakistan is at stake," Bastard added.

RSF quoted the Lahore police report as saying "anti-state and defamatory material against the public functionaries and state departments" was posted on Wahid's Facebook page.

But the report failed to identify the offending material, the group said.

RSF quoted Wahid's lawyer as saying his client was being punished for his criticism of the government and his comments about a recent court decision overturning the death sentence passed on former military ruler Pervez Musharraf in December.

Wahid was charged under two articles of the Prevention of Electronic Crimes Act (PECA), which RSF said was "often used by the authorities to silence journalists who dare to cross the regime's implicit red lines."

"As the traditional media are heavily censored, online platforms have become the only place where Pakistanis can express opinions at variance with the official line," according to the watchdog.

The country is ranked 142nd out of 180 countries in RSF's 2019 World Press Freedom Index.