A nun in her seventies was raped in the early hours of Saturday when a group of six intruders broke into a convent school in eastern India, police said.

The group vandalized the Convent of Jesus and Mary School and then one of them attacked the nun, local police officer Abhijit Biswas said. The victim is now in hospital and no one has so far been arrested.

Chief Minister Mamata Banerjee of West Bengal state, where the school is located, condemned the incident and said "swift, strongest action" would be taken.

According to the BBC, The Archbishop of Calcutta, Thomas d'Souza, said that the intruders could be seen in security footage. He confirmed that there are only three Sisters in the community, and one was molested. "The other two, and a guard, were tied to chairs," the Archbishop added.

Money from the school was stolen, and the chapel vandelised in the attack, he said.

The death of a student after a brutal rape in New Delhi in 2012 caused national outrage and raised public pressure for faster justice in a country where crime against women is rampant but court cases can drag on for years.

Days ago a mob of several thousand people broke into a high-security prison in northeastern India, dragged out a rape suspect and killed him in full public view.

There has also been increasing concern about religious minorities in India. Prime Minister Narendra Modi was forced to promise to protect all minority faith groups following outrage over a wave of recent attacks on Christian institutions in Delhi.

Despite the string of attacks on five churches and a Christian school in the capital, he insisted that his government gives "equal respect to all religions".

"We cannot accept violence against any religion on any pretext and I strongly condemn such violence. My government will act strongly in this regard," Modi said in February.

India is currently 21 on the World Watch List, which ranks the most difficult countries to be a Christian. There were more than 600 attacks on Christian and Muslim groups in the first 100 days of Modi's rule.

(Additional reporting by Reuters)