Incumbent prime minister Peter O’Neill has condemned the killings in Wabag, where two police officers died, after what he described one of the most peaceful elections in recent decades.
Extra police have been sent to the capital of Enga province, where tensions remain high after armed supporters of opposition leader Don Polye and another candidate clashed with assault rifles.
Photos have been circulating on social media of two bodies lying in the streets of Wabag of the alleged gunmen.
The election has been marred by widespread problems with polling, late payments for election officials, allegations of ballot box stuffing and bribery.
Currently Mr O’Neill’s People’s National Congress (PNC) has the largest number of seats but is well short of forming government.
"It is extremely disappointing that in the closing days of the election we are seeing this desperate behaviour," Mr O’Neill said is a statement.
"There is no excuse for the behaviour we have seen over the past two days, and those behind it will be brought to justice," he said.
Thirty-five scrutineers were detained by police at the Wabag counting centre on Friday after destroying ballot boxes and papers.
Police detain election scrutineers after rampage on Friday. Source: SBS / , PNG police
It is the latest and most deadly unrest so far during the election and follows a rampage in Finschhafen last week when supporters of ousted speaker of parliament Theo Zurenuoc burnt down a police station and several schools.
Election observers from the Pacific Forum nations, which includes Australia, have released a critical interim report as embattled electoral commissioner Patilias Gamato was due to return the election writs Monday with less than half of the 111 seats declared.
Mr Gamato has reportedly secured an extension of the deadline to Friday.
Pacific observers praised “the enthusiasm of the general public to engage and be active participants in the exercise of their constitutional rights to vote was apparent” and the role of civil society groups in raising election awareness.
“It is disappointing therefore that a large number of Papua New Guinea citizens were disenfranchised of their constitutional rights to vote, particularly considering the observed high levels of civic awareness and interest in participating in the election,” the report said.
“Several significant challenges were noted, the most serious of which was the alarmingly large number of names missing from electoral rolls.
“These includes (sic) a candidate in one polling station, people who had lived in electorates their whole lives and had voted in previous elections, and people who claimed to have updated their voter details with provincial election offices and/or village and ward recorders.
“There were also many reports from other election observers of the same.”
Destroyed ballot papers in Wabag after election scrutineers go on the rampage on Friday. Source: SBS / , PNG police
The Commonwealth observer interim report also noted “widespread” electoral roll irregularities and called for a review of “all aspects” of the election, which Mr Gamato has said would happen.
Pacific Forum observers like their Commonwealth counterparts were also concerned their recommendations from previous elections about the roll had not been addressed and called on the government to provide “timely support” in future to the Electoral Commission.
Mr Gamato on Friday defended the conduct of the election after post-election violence in four provinces.
“I strongly appeal to losing candidates and their supporters to respect the outcome of their respective electorates and exercise common sense, restraint and maturity,” Mr Gamato said in a statement after again cancelling a scheduled daily press conference.
“Resorting to violence to demonstrate dissatisfaction over the election results is very irresponsible behaviour and indeed unlawful and undemocratic,” he said.
“The appropriate channel through which losing candidates are entitled to dispute and challenge election wins of winning candidates is through the Court of Disputed Returns after the conclusion of the election.”
The backlog of cases after the 2012 election took four years to clear.
Supporters armed with bushknives rally in Wabag on the weekend. Source: Supplied
Mr Gamato statement also praised the role of the media, but attacked some reports for being “misleading”, rejected accusations for 300,000 “ghost voters” and denied the journalists were banned from a counting venue in the capital.
Two weeks ago Mr Gamato received international media attention after securing a court gag order against anti-corruption campaigner Martyn Namorong for alleged defamatory statements critical of the electoral process and calling the commissioner 'Mr Tomato'.
After more then two weeks of counting, only 51 of the 111 seats were declared by Sunday.
The prime minister's PNC has won 18, the rival Pangu and National Alliance parties six each, the People’s Progress Party (PPP) has three while the rest are held by independents or minor parties.
A number of high-profile ministers in the previous O’Neill government have lost their seats but there usually is about a 50 per cent turnover of MPs at elections.
Ahead of the recall of parliament next month, the leading parties have gone into 'camp' to try and form government by luring smaller parties and independents to join them and make up the numbers.
Mr O’Neill has located himself in Alotau in Milne Bay province, incumbent deputy opposition leader Sam Basil's Pangu Party is in Goroka in the Highlands, while the National Alliance Party has set up in Kokopo, the capital of East New Britain.
Parliament is due to be recalled within seven days of the return of writs by the electoral commissioner to the governor general.