More than 1,000 troops were on standby "to step in wherever necessary" under the emergency decree, Prime Minister James Marape announced, a day after the violence broke out.

Marape has earlier pledged to crack down on "lawlessness" Thursday, following riots in which 15 people were killed as angry crowds torched buildings and ransacked shops.

Violence erupted in Port Moresby on Wednesday evening after a group of soldiers, police officers and prison guards launched protests against the government.

Within hours riots had also taken root in the city of Lae, some 300 kilometres (186 miles) to the north.  

Prime Minister James Marape apologised to the country on Thursday, saying the bursts of "lawlessness" would "not be tolerated". 

"I want to speak today, speak to the people and speak to the country," he told a news conference. 

"This is your country as much as it's my country. Breaking the law does not achieve certain outcomes." 

Police Commissioner David Manning confirmed at least 15 people were killed in the unrest.

Port Moresby's largest hospital treated 25 people with gunshot wounds, according to figures provided to AFP, as well as six people with "bush knife" lacerations.

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

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.

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

A smaller crowd gathered earlier outside the prime minister's office in Port Moresby, tearing a security gate off its rails and torching a parked police car.

Beijing has lodged a complaint with Papua New Guinea's government, following reports that rioters targeted Chinese-owned businesses.

Its foreign ministry said two Chinese nationals had been "lightly injured" in the violence.

"We remind Chinese nationals in PNG to pay close attention to the changing security situation on the ground," ministry spokesperson Mao Ning said on Thursday.

The Chinese embassy in Papua New Guinea issued a notice on Thursday reminding Chinese citizens and organizations in the country to strengthen security precautions as a wave of riots, vandalism and looting hits the capital.

In a statement, the embassy said there were localized riots, vandalism and looting, including at number of Chinese stores, and commercial facilities.

At present, there are no reports of deaths of Chinese citizens, however, several were slightly injured, the embassy said.

Australian Prime Minister Anthony Albanese called for calm in neighbouring Papua New Guinea on Thursday, a day after widespread looting and arson left buildings in capital Port Moresby aflame amid reports of several deaths.

Albanese said Australia was monitoring the situation via its high commission and had not received any requests for help from Papua New Guinea, which it regularly supports in policing and security. 

"Our high commission in Port Moresby are keeping a very close eye on what is occurring there, making sure Australians are looked after," he told a news conference. 

Port Moresby resident Maho Laveil, an economics lecturer at the University of Papua New Guinea, said peace had "largely been restored" by Thursday evening. 

"They've chased the looters away, they've stopped the buildings from burning," he told AFP.

National Capital District governor Powes Parkop said the unrest represented an "unprecedented level of strife" in Port Moresby, while local newspaper the Post Courier called it the city's "darkest day".

"What is most important is that we must end this strife," Parkop told a local radio station Wednesday evening. 

"Nobody will be a winner in this type of civil unrest."

Security forces staged a protest inside Papua New Guinea's parliament after noticing their pay had been docked without explanation. 

Although the government swiftly promised to fix what it described as a payroll "glitch", it was not enough to stop disgruntled civilians from joining the fray.

The burst of violence highlights the often volatile nature of life in Papua New Guinea, a country plagued by poverty and high levels of crime.

"You've got this growing resentment, particularly in the capital city, where inequality is very high," Laveil said. 

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