Papua New Guinea's central bank fears 160 million kina ($68 million) of old currency, stolen while being shipped overseas, could be used to influence the country's national elections.

PNG replaced its paper notes with plastic in 2012 and sold some of the discontinued notes to a recycler in Europe.

But the Bank of PNG said a container of notes was hijacked somewhere en route, and was now making its way back into the country across the Indonesian border.

The Bank of PNG's governor, Loi Bakani, said it was working with Indonesian authorities to find and return the notes.

"We are working together with banks there and authorities on the Indonesian side to get the money out of there," he said.

"The unfortunate thing is that if we are not careful, the money [may] find its way into parts of Papua New Guinea where our innocent people will think it's the real money — plastic money — and accept it.

"It is part of the money that was demonetised and we shouldn't accept it as legal tender anymore. It is illegally being brought back. We sold it and ... we cannot pay any money for it."

Candidates across PNG are campaigning heavily for election in the country's national poll in June.

Mr Bakani said it was important that the stolen money not be used to fund any campaigns or influence voters.

"Its election time I know. I hope some of this money is not floating around with the public," he said.

"Because of election times, circulation of money goes very fast. Meaning that a lot of money is thrown around for supporters to access goods and services.

"We hope that our people can be alerted about this and make sure that if they see or get hold of this money, they should not accept it."

The Bank of PNG is publishing the serial numbers of the stolen notes and has asked Papua New Guineans to check any paper notes they find.

Mr Bakani said the PNG Border Authority had already intercepted some of the old currency at the Indonesian border.