Philippines President Rodrigo Duterte said on Monday that Emmanuel "Manny" Pacquiao should name corrupt government offices to prove that the boxer-turned-lawmaker is not just politicking ahead of a presidential election next year.

The comments were the latest chapter in a surprise war of words between the president and Pacquiao who is seen as being among his strongest backers and a possible successor when the single six-year term he is allowed expires next June.

The firebrand Philippine leader said Pacquiao had criticised corruption in his government and threatened to expose the boxing champion as a liar.

"I'm not saying there is no corruption, so expose it," Duterte said in a televised late night national address. "If you don't do that, I will expose you daily as a liar ... I know you from way back."

Using an expletive in his strongest language yet against Pacquiao, Duterte said if he did not reveal corruption, he would be "playing politics" and pledged to take action against any erring officials.

It was not immediately clear what officials he was urging Pacquiao to expose, or why. Pacquiao has not publicly been speaking about any allegations of high-level corruption in recent days.

Pacquiao, the acting president of Duterte's political party, was not immediately available for comment outside office hours.

Pacquiao, 42, has long been among Duterte's strongest supporters, backing his bloody war on drugs and bid to re-introduce the death penalty. The eight-division champion has yet to announce his presidential bid.

Early this month, Duterte criticised Pacquiao's "shallow" foreign policy knowledge, after the senator said he found the leader's stand on the South China Sea as "lacking" and "disheartening".

Duterte remains popular in the Philippines. Political allies are urging him to run as vice president when his term ends. His daughter - a long term aide - is also seen among his possible successors.