Police declared a curfew in eastern Sierra Leone on Monday after political violence ahead of next month's presidential second-round runoff which left several people injured.

In the mining town of Kono, a centre of the illegal diamond mining trade which fuelled Sierra Leone's 1991-2002 civil war, police fired tear gas and shots into the air to disperse more than a thousand supporters of the ruling Sierra Leone People's Party (SLPP) and the opposition All People's Congress (APC).

"We succeeded in bringing the situation under control. A good number of those who sustained injuries were taken to the Kono government hospital," police commander for eastern Sierra Leone Santigie Koroma, told Reuters.

"I have declared a curfew from 16h00 to 06h00 with effect from today," he noted

Tensions are running high ahead of the September 8 runoff vote after the APC won control of the national parliament in August 11 legislative polls, held at the same time as the presidential first round. They were the first elections since UN peacekeepers left the West African country in 2005.

In the first round, Ernest Bai Koroma of the APC won 44%, followed by Vice President Soloman Berewa of the SLPP on 38%. Koroma has already received the backing of the third-placed PMDC candidate Charles Margai, who polled 14%.

The elections are seen as a test of Sierra Leone's recovery from more than a decade of civil war, one of Africa's most brutal conflicts which shocked the world with images of drugged child soldiers and mutilated civilians.