WARSAW (Reuters) - Poland's largest opposition party has called for a rerun of regional elections held last Sunday because a computer failure has left the country with no word of the final results.

President Bronislaw Komorowski dismissed the suggestion as the height of insanity. The state election commission, the PKW, said on Saturday it did not know when the final results would be announced. The votes are being counted manually.

Poland, known in recent years for its political stability in an otherwise volatile region, has been shaken by the failure of the computer system.

"The breakdown of the system for counting votes is a scandalous occurrence, an embarrassment," President Komorowski told state television late on Friday.

"It is the peak of insanity to demand that the president take actions that would lead to a repeat of the vote," he said.

Jaroslaw Kaczynski, the leader of the Law and Justice (PiS) party, the second largest force in parliament, has called for a repetition of the vote, a call joined by the leftist SLD party.

An exit poll on Sunday showed the PiS has taken the lead in the vote, signaling a possible shake-up ahead of a national vote next year.

Komorowski, who postponed his official visit to Japan because of the problems with the vote, said only courts could void the results of the elections.

On Wednesday, the PKW said someone hacked its web page, but it said this did not put the results of the vote at risk.

The following day, demonstrators from a protest organized by the far-right party Ruch Narodowy stormed the headquarters of PKW demanding its dismissal.

That forced the PKW to temporarily suspend its work. Police arrested several of the demonstrators.

Poland holds regional elections every four years to choose mayors, provincial assembly members and other local authorities.

(Reporting by Marcin Goettig; Editing by Stephen Powell)