At least 23 people were killed on Friday when ethnic conflict flared in Kyrgyzstan's second-largest city Osh, the worst outbreak of violence in the Central Asian state since the president was overthrown in April.

The interim government in Kyrgyzstan, which hosts US and Russian military bases, declared a state of emergency in four southern regions after hundreds of youths battled with guns and steel bars, setting shops ablaze in the city.

The government, led by Roza Otunbayeva, sent troops and armoured vehicles to quell gangs roaming the streets with sticks, stones and petrol bombs after a night of violence.

'Regrettably for us, we're clearly talking about a stand-off between two ethnicities. We need (to muster) forces and means to stop and calm these people down, and this is what we are doing right now,' Otunbayeva told reporters in the capital Bishkek.

A Reuters correspondent said a group of up to 300 mainly young and aggressive people was moving from the Kyrgyz part of Osh to the city's quarters populated mainly by ethnic Uzbeks.

'As they move, they set cafes and shops on fire,' she said, adding that no police or armed forces were seen.

Otunbayeva said crowds of 'weird and suspicious-looking people' were streaming down to Osh 'from all directions.' She did not mention the ethnicity of these people. Political tensions between the agricultural south and the north of Kyrgyzstan exist alongside rife ethnic and clan rivalries.

'The situation remains complicated,' she said. 'Attempts are being made to block practically all the roads leading to Osh. This is what our security forces are trying to do,' she said.

The violence occurred in the southern power base of former President Kurmanbek Bakiyev, deposed in April by a popular revolt. Bakiyev's supporters briefly seized government buildings in the south on May 13, defying central authorities in Bishkek.

Renewed turmoil in the impoverished former Soviet republic will fuel concern among regional players Russia, China and the United States, which uses its air base in the country's north - about 300 km from Osh - as an Afghan supply route.

Russian President Dmitry Medvedev told a regional security summit in Uzbekistan's capital Tashkent that Moscow wanted a swift end to the unrest. Chinese leader Hu Jintao echoed him, saying: 'China continues to help Kyrgyzstan as much as it can.'

At least 23 people were killed and 338 hurt during Friday's violence, the Health Ministry said. Many suffered gunshot wounds. Officials said the riots were sparked by a fight, possibly in a casino, which fast escalated into ethnic clashes.

'Today our multinational population once more finds itself in a situation that requires every one of us to display extraordinary restraint, wisdom and ability to emerge from conflict peacefully, by way of negotiation,' she said.

Ismail Isakov, defence minister in the interim government and a recently appointed special representative for southern Kyrgyzstan, and Interior Minister Bolot Sherniyazov flew to Osh, a city of over 200,000 people in the volatile Fergana valley.

Kyrgyzstan has sent reinforcements to tighten control of its border with Uzbekistan, Salkyn Abdykariyeva, spokeswoman for the country's border police, said by telephone from Osh.

Uzbek President Islam Karimov, speaking at the regional summit in Tashkent, said events across the border were 'an internal matter for Kyrgyzstan' but that Uzbekistan was prepared to offer help in stabilising the situation.

Kyrgyzstan, which won independence with the collapse of the Soviet Union in 1991, has been in turmoil since the revolt that toppled Bakiyev on April 7, kindling fears of civil war.

Ethnic unrest between Kyrgyz and Uzbeks is a concern in the Fergana valley where Kyrgyzstan and Uzbekistan intertwine. In 1990, shortly before the collapse of the Soviet Union, hundreds of people were killed in ethnic clashes near Osh.

On May 19, two people were killed and 74 wounded in clashes between Kyrgyz and Uzbeks in the city of Jalalabad. On the same day, Otunbayeva said she would rule the country until the end of 2011, scrapping plans for presidential polls in October.

Jalalabad has also been the scene of fierce clashes between supporters of the interim government and those of Bakiyev, who is in exile in Belarus.

Of Kyrgyzstan's 5.3 million population, ethnic Kyrgyz make up 69.6 percent, Uzbeks 14.5 percent and Russians 8.4 percent.

In the south, Uzbeks comprise about 40 percent of the 1 million population in the Jalalabad region and about 50 percent in the neighbouring region of Osh.-Reuters