Opposition parties in India are holding protest rallies on Monday against a controversial citizenship law backed strongly by the government of Prime Minister Narendra Modi despite demonstrations across the country.

More than 100,000 people joined what police described as a peaceful march against the law in the southern city of Chennai, a spokesman for the DMK regional party said.

Some demonstrations against the law over the past two weeks have erupted in violence and clashes with police leading to the deaths of at least 22 people, most of them in northern Uttar Pradesh state.

The country's main opposition Indian National Congress party plans a sit-down protest near the mausoleum of Mahatma Gandhi in Delhi later Monday.

The Citizenship Amendment Act, 2019, allows Hindu, Sikh, Buddhist, Jain, Christian and Parsi immigrants from three neighbouring Muslim-majority countries to avail of fast-track citizenship.

Critics say it goes against India's secular constitution, but Modi's Bharatiya Janata Party (BJP) government says it does not affect any Indian citizens and is not against Muslims.

Modi defended the bill again on Sunday, and said that opposition parties were spreading ‘lies’ to incite people.

Protests are being held against the citizenship law and a proposed National Register of Citizens (NRC) by students, Muslim community members, civil society groups and opposition parties across the country.

Under the NRC exercise every resident would have to show documents proving they are Indian citizens.