The first public trial into the annulment of the Austrian presidential run-off vote began at Vienna's Constitutional Court on Monday.

Over the next four days, the court will hear testimony from around 90 witnesses to determine whether or not the run-off vote will need to be partially or totally repeated.

The far-right, populist FPÖ party submitted the legal challenge, saying there had been numerous irregularities with the postal ballots. According to their court challenge, hundreds of thousands of ballot envelopes were opened prematurely - increasing the risk of tampering - and some of the votes were tallied by unauthorized people.

Postal ballots in the May 22 run-off election pushed former leader of the Green Party, Alexander Van der Bellen - who ran as an independent - barely ahead of FPÖ candidate Norbert Hofer. The margin of victory was under 1 percentage point, or roughly 31,000 votes.

Van der Bellen (R) narrowly beat out Hofer (L) with a margin under 1 percentage point.

Witnesses take the stand

On Monday, the first witnesses confirmed that the outer envelopes of around 14,000 absentee ballots had been opened on Sunday May 22 from the large Innsbruck-Land constituency. The postal ballots were not to be counted before 9 a.m. (0700 UTC) on Monday May 23.

"There were preparatory actions, but the envelopes were opened only at 9 a.m.," one witness told the judges, according to Austrian news outlet oe24. The constituency reportedly received oral permission from the Electoral Commission, but it was not documented.

According to oe24, other witnesses gave explanations for bringing in additional staff to count the votes, with one claiming it would have taken "30 hours" to count all the votes without additional help.

"It is not possible to properly process so many ballots," he told the court.

A cancellation of the election would be a "disgrace," Interior Minister Wolfgang Sobotka told the weekly newspaper Österreich over the weekend.

He rejected any possible errors in his ministry, saying: "The sloppiness occurred within the district or municipal authorities, not with us."

The court will announce their decision before July 8, when the President-elect Van der Bellen is due to be sworn in.

rs/kms (dpa, Reuters)