Hundreds of shrimp farmers in Thailand have rallied outside the prime minister's office in Bangkok to protest against a ban on inland shrimp farming.

The farmers who are mostly from central regions of the country say they will stay in the capital until their grievances are heard by the government.

The cabinet approved the ban last week because of fears that the salty water used by shrimp farmers would harm the quality of farmland available for other uses.

Shrimps are a major Thai export and the ban could cut lucrative incomes for farmers who are benefitting from recent increases in shrimp prices.