According to the National Broadcasting Corporation of PNG, its police reporter Kayok was travelling with a policeman friend when a mobile police unit pulled them over at a service station.
The officers in the unit reportedly began assaulting Kayok's friend.
Kayok intervened and after the perpetrators found out he was a journalist they reportedly broke his nose and smashed his mobile phone.
In an ABC radio interview, Pacific Freedom Forum chairman Titi Gabi said Kayok and his friend were on the way back from an evening press conference with trade unions before they were assaulted by police.
"Sadly, the policemen that bashed him and his police mate, they were the coppers that were flown into Port Moresby from Mount Hagen," she told the radio station.
"And the policeman he was with is a Port Moresby-based policeman.
"But since the impasse in PNG politics, there's been a conflict between those two sections of police."
While media veterans wait for an official government and police response to the incident, Gabi discussed other acts of intimidation.
"There've been several, some we have talked about, others have been via telephone calls, others have said they've got a visit from security staff of certain MPs, others have unfortunately been getting from their own media organisations," Gabi said.
"There's an unusually high reportage of threats against the media lately. It's worrying."
PNG Media Workers Association chairman Susuve Laumaea has condemned the assault on Kayok as barbaric.
"The media must be allowed to do its job without fear of intimidation from anyone, if the public is to rely on it for accurate and balanced information," he said, according to NewsPNG.org.
In early March, the Post-Courier reported that a policeman had threatened to blow up one of its journalists with a hand grenade.
The assault on Kayok was only a few days after men from Highlands-based police units assaulted nine Port Moresby-based police, with two requiring hospital treatment.