At least 21 people have been injured in Nicaragua as protesters opposed to the construction of a $50bn shipping canal clashed with police, authorities said.

Protesters are concerned that their homes could be threatened by the canal which will run through rainforest and at least 40 villages.

Police fired rubber-coated steel bullets and tear gas at hundreds of demonstrators on Wednesday as they tried to clear a roadblock on the Pan-American Highway in El Tule, 260km from the capital, Managua.

Aminta Granera, Nicaragua's director general of police, said 15 police officers and six civilians were injured as they confronted 300 residents.

Organisers of the protest said at least 40 demonstrators were injured.

Thirty-three protesters were detained by police, Granera said, adding that they used guns, machetes, stones and sticks to attack the police.

Organisers said their demonstration was peaceful.

Nicaragua on Monday announced the start of the canal project, which is backed by a Hong Kong-based company.

The environmental, technical and financial studies of the 280km long route have been kept secret.

The canal is expected to displace around 30,000 people, mainly poor farmers and native people, but could be a major financial boon for the Central American nation.

The proposed canal would pass through Lake Nicaragua, Central America's largest lake, and would be more than three times longer than the Panama Canal.

Source: Agencies