<p>About 20 houses have been burnt down in riots by cashew nut farmers and other protesters in southern Tanzania, the local MP has told the BBC.Faith Mitambo said two buildings at her home in Liwale town had been set alight and that other houses targeted belonged to members of the ruling CCM party.</p> <p>The trouble began after payouts being made to farmers for their crop were less than the price agreed last year.More police have been deployed to the region to stop further unrest.Ms Mitambo, who was in the capital, Dodoma, at the time, told the BBC Swahili service she was travelling down to her constituency to assess the situation.She had been told the protests, involving groups of young men, began in villages on Tuesday morning and reached Liwale town by the evening.</p> <p>A resident of Liwale told the BBC that on Wednesday there was a sense of fear in the town and police had fired tear gas in the market to stop crowds gathering.He said a police helicopter was flying over the town, which is about 500km (310 miles) south of the main city of Dar es Salaam.Thousands of small-scale cashew nut farmers in Tanzania - who usually begin to harvest in October - sell their crops to co-operative societies at an agreed price.</p> <p>The BBC's Erick Nampesya in Dar es Salaam says this was set at 1,200 Tanzanian shillings ($0.74; £.048) per kg.Towards the end of last year, the farmers received the first instalment of the money they were owed.But when representatives from the co-operative societies went to the Liwale district on Tuesday to pay out the second and final instalment, the terms had changed.The farmers were offered half or less than half of the outstanding money as they were told that the prices had fallen on world markets.Ruling politicians, who the farmers blame for not helping them, became the target of their anger, our reporter says.Farmers have long complained about the instability of the prices paid for their cashew nut crops - as it fluctuates from season to season, he says.Police spokesperson Advera Senso told the BBC a special team had been sent to Liwale from Dar es Salaam to investigate and assist with making arrests.</p> <p> </p>