Political scientist: "Nothing has been decided yet. It is very exciting".

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STOCKHOLM (AFP) - Sweden's centre-right coalition's bid to retain its overall majority hung on a knife-edge Wednesday, amid media reports it was less than 300 votes short as counting of late ballots began .

Prime Minister Fredrik Reinfeldt's four-party bloc fell three seats short of a majority with just over 49 percent of the vote in Sunday's general election, as an emerging far-right swept 20 seats.

But with about 60,000 ballots cast abroad left to count, Swedish media reported that to secure a majority the coalition only needed 42 extra votes in the central Dalarna region, 92 in neighbouring Vaermland and 164 in the southwestern Gothenburg region.

"Nothing has been decided yet. It is very exciting," political scientist Olle Folke told the Expressen daily.

Reinfeldt himself said Monday he did not consider the battle for a majority lost, insisting "we must wait for the final election result."

Although the prime minister has ruled out cooperating with the far-right, anti-immigrant Sweden Democrats, their presence in a narrowly-split house with no majority has plunged the country into political instability.

But the approximately one percent of votes still uncounted could potentially tip the balance in the government's favour, thus dramatically shrinking the impact of the far-right's parliamentary debut.

"The result so far is a bit disproportional. If the late votes land in a certain way, theoretically at least, the (opposition) Social Democrats could lose three seats," Svante Linusson, a mathematician at Stockholm's Royal Institute of Technology, told AFP.

The government minority, he explained could simply be the result of Sweden's complex electoral system, where seats in parliament are based on the number of seats each party wins in regional assemblies.

In each region, slight mistakes in proportionality are introduced when rounding up or down votes to fit mandates, and at a national level those mistakes can add up to be significant, he said.

The mathematician said that the system could easily mean "that the centre-right will in total have most votes but still no majority in the parliament."

The full result is expected early Thursday.