By Jill McGivering BBC South Asia correspondent

Police in the southern Indian state of Tamil Nadu have arrested 10 people who were organising a mass baptism in the state.

Thousands of low-caste Hindus - known as Dalits - are to be converted to Christianity and Buddhism.

It is being planned by Christian and Dalit groups to defy a tough new anti-conversion law.

The vaguely worded law is technically against forced conversions but Christian leaders say its aim is to stop all conversions.

Friday's planned mass conversion is seen as an important test of the new law.

About 3,000 Dalits are expected to gather for an open air ceremony to convert to Christianity or Buddhism.

They haven't applied to the local magistrate to approve their conversion as the new law now requires.

Arrests

The police have already taken action.

Ten organisers were arrested during the night and the original site has been cordoned off.

Christian leaders say they will go ahead with the ceremony in another venue.

One British Christian, who has come to India to monitor the event, said the arrests by police showed the law was aimed at stopping all conversions, not just those involving coercion or inducement as its supporters have argued.

Alarm

Christians, Buddhists and Muslims are small minorities in the state but the recent conversions of whole low caste Hindu communities to other religions has alarmed right-wing Hindu organisations.

Many Christians say the new law is unconstitutional because it compromises the right to religious freedom.

They are also concerned the new law will be used to intimidate religious minorities and could be introduced in more states.

Some Hindu leaders accuse evangelical Christians of bribing the poor by offering inducements to convert and they see the law as a way of protecting them.

But Christian leaders insist the conversions are voluntary.