Police in DR Congo Saturday fired on an opposition rally, injuring six protesters denouncing the extended rule of President Joseph Kabila, a lawmaker said.

"The police fired on our militants, injuring six of them, even though we had permission to hold our meeting," said Delly Sesanga MP, president of Envol, a member of the opposition coalition.

He claimed that he himself had been "assaulted and kidnapped for more than three hours" during the incident in Kenge, east of the capital.

However, according to a statement by the national police, only one protester was wounded in the head, and that was caused by stones thrown by other demonstrators.

The police "fired in the air to disperse a crowd that had not been approved by Kenge City Hall", said Emery Kaputa Vita, deputy governor of Kwango Province, where Kenge, some 270 kilometres (170 miles) from Kinshasa, said.

The opposition coalition and other citizens' movements are against the vote schedule published by the electoral commission in the DR Congo.

It predicts that the presidential election will be held on December 23, 2018, extending Joseph Kabila's term as head of the country by a year.

Kabila was scheduled to have stepped down in December 2016 after a constitutional maximum of two terms in office.

Those against President Kabila's stay in power are mobilising force his departure by 31 December, 2017 at the latest.

On Thursday, the European Union, the United States, Switzerland and Canada expressed "concern" at the state of freedoms of expression and assembly in the DR Congo, following a day of protest and a crackdown by security forces.

The opposition are considering a "peaceful demonstration" in Kinshasa on November 28, according to a letter seen by AFP.