SYDNEY (Reuters) - Tourists, expats and business owners in Papua New Guinea joined locals in hunkering down for a night of potential violence amid fears of "payback" against the nation's police force after it opened fire on a group of students, wounding several.

"This is going to get worse before it gets better," Greg Anderson, executive director of the Papua New Guinea Chamber of Mines and Petroleum said from Port Moresby, where a protest against the government of Prime Minister Peter O'Neill erupted on Wednesday. "Incidents like this trigger paybacks, which could easily spiral out of control."