Police have clashed with farmers blocking a highway in the southern Philippines to demand drought relief from the government, leaving at least two demonstrators dead and dozens of people injured.

Scuffles broke out and shots were fired when security forces moved in to disperse about 6,000 farmers and their supporters, who were protesting for the fourth day in a row in Kidapawan, the capital of Cotabato province, police sources and the Cotabato governor, Emmylou Mendoza, said.

Mendoza said two protesters had been killed and a journalist at the site counted 13 people injured. The provincial police chief, Alexander Tagum, said at least 23 officers had also been hurt.

Two had head injuries and were in critical condition, said national police spokesman Wilben Mayor.

One of the farmers injured in the scuffles Photograph: EPA

The farmers, who have been demanding financial aid and rice during a drought which has lasted for months, said the police fired at them. Police said some of the protesters were armed and fired first.

Mayor said the police were still gathering information. Before shots were fired, police had given the protesters an ultimatum to leave. After negotiations failed, they began pushing the farmers away with their shields, but the farmers fought back by throwing stones while firefighters turned their hoses on them.

Leftwing groups, which support the farmers’ demands, quickly condemned the police for using force.

“The farmers were calling for rice, but bullets rained on them instead,” said Terry Ridon of the Youth party.