By Matt Siegel

SYDNEY (Reuters) - Aviation, maritime and public transport workers in Papua New Guinea went on strike on Thursday before a no-confidence vote in Prime Minister Peter O'Neill, who has refused to resign over corruption allegations.

The strikes have effectively cut off Papua New Guinea after a groundswell of political unrest in recent weeks in the rugged, mountainous country, which relies heavily on air travel.

Friday's scheduled no-confidence vote against O'Neill has sparked fears of more unrest. Last month, weeks of peaceful protests by university students ended in violent clashes with police in which officials said nearly 40 people were injured, including four with bullet wounds.

Although the strike in the three main urban centers of Port Moresby, Lae and Mount Hagen involves more than one industry, it is the aviation strike that is having the greatest impact, said Martyn Namorong, head of the PNG Resource Governance Coalition.

Poor roads through the thickly forested highlands that separate its few large cities mean that travelers are effectively stranded without air travel, Namorong told Reuters.

"For those who are traveling it's a major impact on people about to commute throughout our country because our country is severely dependant on air transport," he said by phone from Port Moresby.

Human Rights lawyer Moses Murray, a spokesman for the strikers, told Radio New Zealand that the action was peaceful and focused on the aviation, maritime, public transport and banking sectors.

O'Neill came to power in 2011 promising to rein in corruption but is facing allegations he authorized millions of dollars in fraudulent payments to a leading law firm.

In 2014, an anti-corruption watchdog issued an order for his arrest over the incident, which O'Neill denies. He refused to submit to the warrant and ordered the watchdog stripped of its funding.

At least one academic has accused O'Neill of using the power of his office to avoid facing charges.

The strikes have contributed to a growing sense of unease in Port Moresby ahead of Friday's no-confidence vote, said Noel Anjo, a leader of the student protests.

Papua New Guinea is developing lucrative resource projects with energy majors ExxonMobil and Total that have made it a major gas producer.

However, corruption and violence are endemic in the island nation of seven million people, raising concerns about its long-term stability.

(Reporting by Matt Siegel; Editing by Paul Tait)