(AFP) - Troops patrolled the streets of Papua New Guinea's capital on Friday, under a state of emergency following riots that killed 16 across the country's two largest cities.

Prime Minister James Marape has pledged to restore calm after angry crowds swelled in Port Moresby on Wednesday evening, smashing windows, pillaging shops and setting buildings ablaze.

Marape said rioters would "pay the price" for the outbreaks of "lawlessness", declaring a 14-day state of emergency for the capital on Thursday evening.

With 1,000 soldiers placed on standby to bolster security, many of the city's bank branches, petrol stations and grocery stores began re-opening Friday.

"Shops have opened, fuel stations have opened, public transportation is open. People are moving again. There's been a sense of peace," Port Moresby resident Maho Laveil told AFP.

"There's an increased level of police and military around the city," the economics lecturer added.

"I think the risk is at night."

Violence first broke out in Port Moresby after a group of soldiers, police officers and prison guards went on strike after noticing unexplained deductions in their pay.

With disgruntled citizens joining the fray, the unrest soon spread to the city of Lae about 300 kilometres (186 miles) to the north.

Police and health officials said at least 16 people had been killed across the two cities, according to updated figures released Friday.

Marape conceded security forces had a "genuine cause of concern", and his government swiftly promised to fix what it described as a payroll "glitch".

But he warned that "lawlessness and recklessness" would not be tolerated.

"This is not the first time members of our disciplinary forces have gone rogue," he told reporters Thursday evening, referencing a 2018 pay dispute that ended with security staff smashing up the country's parliament.

"I want to indicate to our country enough is enough. Enough is enough."

- 'Waves of casualties' -

AFPTV footage showed looters in the capital dashing into stores through smashed glass windows, stuffing stolen goods into cardboard boxes, plastic buckets and shopping trolleys.

One man was seen lugging an entire chest freezer away on his shoulders.

Buildings and cars were set alight, AFPTV footage showed, stirring up thick plumes of black smoke that hung over the worst-hit parts of the city.

City Pharmacy Limited, one of Papua New Guinea's largest retail chains, said prescription medicines had been stolen from its ransacked stores.

"We urge the public not to buy these products. If anybody uses these products, it will be at your own risk," the company said in a statement.

It also made an "urgent appeal" for Port Moresby residents to return stolen shopping trolleys.

Port Moresby General Hospital said it was inundated by "waves of casualties", including 30 people with gunshot wounds, six others with "bush knife" lacerations, and five people with burns.

The US embassy in Port Moresby said shots were fired near its compound as police tried to "disperse groups of looters".

China's foreign ministry lodged a complaint with Papua New Guinea's government, following reports that some rioters had targeted Chinese-owned businesses.

© Agence France-Presse