Extra police have been flown in to the capital but there could be periods of time when mobs rule the streets, as evident from the recent riots in Lae.
"While we expect the December 9 protests to be localised to the governmental areas of Port Moresby, political tensions can rise with little notice and at any time throughout Papua New Guinea," the US Embassy in Port Moresby said.
"Pay close attention to your personal security at all times and monitor the media for information about possible new safety or security risks.
"Avoid large crowds, public gatherings and political rallies, as these may turn violent."
The Supreme Court has delayed the judgement to Monday according to recent reports.
The various security alerts over possible unrest in Port Moresby are consequently more valid for next week.