Somare, one of PNG's founding fathers, lost his reign as prime minister to Peter O'Neill through a controversial parliament vote on August 2 while on four months of extended medical leave.

The vote was determined to be unconstitutional and void in a 3:2 decision of the Supreme Court yesterday, while the O'Neill coalition passed amendments in parliament in an attempt to keep O'Neill as prime minister.

Neither leader was sworn in as prime minister following the court case but O'Neill was denied access to the nation's governor general by police last night.

There were reports of gunfire at parliament house at some stage afterwards.

"Trying to forecast one week ahead is quite a challenge because we wake up this morning and we basically have two prime ministers, two police commissioners and two of everything else," Institute of National Affairs director Paul Barker told PNGIndustryNews.net.

He said last night there were separate police factions aligned to O'Neill and Somare, while Governor General Michael Ogio had his own police unit to protect him from everyone.

Barker said Somare was likely to be sworn in as leader in Port Moresby at around 1pm local time today but he expected other difficulties as the twice-delayed budget was also due to be passed in parliament today.

"Both sides really need that budget to be passed because they need the electoral commissioner to be able to get the allocated 180 million kina to prepare for the elections [due in mid-2012]," he said.

He did not expect major instances of civil unrest but said the different police factions were a worry.

But there is also a risk either the Somare camp or the O'Neill coalition will grab at opportunities to access more government funds ahead of what will be a fiercely contested election.

"What a lot of people will fear is that it's just a chance for one or the other to get their hands on the kitty for the next few months," Barker said.

"Unfortunately both sides have a limited number of angels in them."

A wave of looming contempt charges facing front bench members of the O'Neill coalition could finalise the reinstalment of the Somare government.

Belden Namah, who was deputy prime minister under the O'Neill government, is already facing contempt charges before the Supreme Court this morning for his involvement in a failed attempt to suspend the court's Chief Justice Sir Salamo Injia last month.

A source aligned with the Somare camp told PNGIndustryNews.net its lawyers would press for Namah to be immediately jailed for breaching his bail conditions.

Namah, along with up to 64 other members of parliament, voted on Friday to retroactively rescind the leave of absence granted to Somare earlier this year.

The O'Neill government passed further amendments to secure O'Neill's position as prime minister yesterday while the Supreme Court judges were stating their findings.

The parliamentary actions could be deemed to be contempt of the recent Supreme Court case on the legitimacy of the O'Neill government and Namah had already been warned.

"If he is put behind bars, I think it will send a chill down the spine of everyone on the other side," the source said.

If sentenced to more than nine months of prison, Namah will not be able to stand for election for three years, which would be a severe blow to the O'Neill coalition.

The source expects the National Executive Council members of the coalition, including O'Neill, will all be targeted for further contempt charges.

The Somare camp already announced its new cabinet, with John Pundari - known for criticising BHP Billiton over its past operation of the Ok Tedi mine - flagged to return as mining minister.

Francis Potape is expected to return as Petroleum and Energy minister under the resurrected Somare government.

Neither Barker nor the source expected significant impacts to the active mining and petroleum companies under a reinstalled Somare government.

The O'Neill government previously caused some fears in the sectors by flagging possible changes to the country's resource ownership laws but it backtracked on the stance in recent months due to a widespread industry outcry.

While 76-year-old Somare has lost considerable weight this year, he has made a remarkable recovery from operations on his heart, lungs and kidneys in Singapore.

In late June, his retirement from politics was prematurely announced by his son Arthur, back when the outlook was more grim.

Somare previously signalled ambitions to at least lead PNG through to the next election.