CHARLOTTETOWN -- A slim majority of Prince Edward Island voters have rejected a switch to a proportional representation electoral system, though it remains unclear how the province's new government will respond.

Voters in Tuesday's general election were also asked to answer a referendum question: "Should Prince Edward Island change its voting system to a mixed member proportional voting system?"

All parties had accepted that whichever side won more than 50 per cent of the votes cast in at least 17 of the 27 ridings would be declared the victor.

By late Tuesday, the "No" side had captured close to 51 per cent of the total votes, with the "Yes" side holding 49 per cent. Two advance polls had yet to report.

However, neither side had won 17 ridings, with the "Yes" victorious in 15 and "No" taking 12.

Gerard Mitchell, the referendum commissioner, said in an interview earlier in the evening that if neither side reached the 17-seat threshold, "it means it wouldn't be binding on government."

"If it's close enough then I guess government, or whoever is governing, will have to make a decision."

The premier-designate, Tory Leader Dennis King, said Tuesday he would "leave it up the legislature."

Peter Bevan-Baker, the leader of the Green Party, which took eight seats and will form the opposition, said the result was "agonizingly close."

"I really would have liked P.E.I. to have been a pioneer here in adopting proportional representation," he said.

"But I think it is inevitable that proportional representation is coming. We are not going to be the ones leading that charge in Canada but we came very close and Islanders showed there was a level of discomfort with the status quo."

The leaders of all four political parties had said during a leaders' debate they would consider the result binding if the thresholds were reached, but it was less clear what would happen if they were not achieved.

The "Yes" option would mean a slimmed-down roster of 18 legislators in redrawn electoral districts, while citizens would also cast ballots for nine other legislators from lists the parties create.

These "party list" seats would then be assigned proportionately based on the popular vote each party received on the second part of the ballots.

A "No" win would retain the first-past-the-post system with 27 legislators elected.

John Barrett, a spokesman for the "No" side, said he considered the result decisive and that the province should put the idea of a mixed member proportional system to rest.

"I'm pleased that first-past-the-post will continue as our electoral system," he said.

He noted that the rural areas of the province had voted decisively, as they feared losing their representation under the new system.

"Fifty-one per cent is a win and we'll take it," he said.

However, Brenda Oslawsky, a spokeswoman for the "Yes" side, said that "we're pleased we won a majority of the districts."

"We think with two leaders who've come out in favour of mixed member proportional ... that they will look to strike a committee or bring in a citizens assembly to find a way to bring a proportional representation coming to the Island."

Advocates of proportional representation on the Island argued a large part of the population has been under-represented in past legislatures, which have often swung with lop-sided results for either the Liberal or Conservative parties.

The "No" side argued the proposed system left too many questions unanswered, such as how parties will choose their lists of candidates.

It also warned the system risks creating a series of unstable, minority governments without a fair representation of rural voters.

Political scientists struggled to assess the outcome of the historic vote in the lead-up to the referendum, noting the two campaigns were relatively low key.

Don Desserud, who teaches at the University of Prince Edward Island, has said many voters found themselves making up their minds on the referendum as they cast ballots for a new government, without having carefully considered a potentially historic change.

Voters in British Columbia rejected making such a change to a mixed member proportional system in December.

Prime Minister Justin Trudeau promised to abolish the first-past-the-post federal voting system during the 2015 election, but he later abandoned the plan, saying Canadians were not eager for change.

However, Quebec's new CAQ government, which campaigned in part on the issue, has said it would move to adopt a mixed member proportional system before the next provincial election in 2022.

-- By Michael Tutton in Halifax.