A Swiss woman has been charged with assault after slapping an Afghan migrant who allegedly groped her during a New Year's Eve street party.

The unnamed woman, 21, was said to have left the man with a broken nose when he reportedly groped her during a party at the City Hall in the Austrian capital Vienna.

After news of the charges against her were made public, a wealthy Swiss businessman has stepped in with an offer to pay the fine on her behalf.

Former MP and bigwig of the conservative Swiss People's Party (SVP) Christoph Blocher was one of many that defended the actions of the 21-year-old woman.

The 21-year-old woman claimed to have been groped by the man during New Year's celebrations at City Hall, Vienna, Austria (pictured)

Blocher, an industrialist and influential figure in Swiss politics despite his retirement, said: 'If the woman gets punished, I will gladly pay the fine.'

He added: 'How should a woman defend herself otherwise if that is not allowed?'

Swiss businessman Christoph Blocher has offered to pay her fine

Blocher admitted that he would have reacted in the same way if someone had tried to steal his wallet, for example.

Local media alleged that a 20-year-old Afghan suspect was part of a migrant gang who were allegedly assaulting women in the crowd during the New Year celebrations.

According to the Vienna Police, the Swiss woman reacted angrily when she was fondled by the migrant and smacked him full in the face.

Witnesses called the police at 1.30am to report the incident.

At the same time, the suspect went to see cops on the square as he reportedly had a broken nose.

He was taken to hospital to be treated and a criminal charge for sexual harassment was filed against the 20-year-old Afghan, and a criminal complaint against the victim for GBH.

Under Austrian law, the police have a duty to file a criminal complaint when the alleged offence is of such severity that prosecutors have no choice but to pursue it.