Hundreds of Cambodians armed with farm tools and metal bars have rioted through a Phnom Penh slum after a child was hurt by falling timber as authorities tried to pull down a squatter's home.

Several buildings have been torched and a corrugated metal fence, that authorities had put up to contain the slum, has been torn apart.

The injured child was taken unconscious to a nearby hospital and her condition is unknown.

The slum has been a source of tension, punctuated by violent outbursts, for weeks as city authorities try to evict more than 1,000 families to clear the land for a private company to develop.

Hundreds have refused to resettle on a site some 22 kilometres outside the capital, complaining that the land offered to them is unlivable and too far away from markets or work.

Instead, the squatters have for weeks lived under crude shelters of plastic sheeting and bamboo poles amid the debris of their dismantled homes.

Rights groups have repeatedly complained about the forced resettlement, and two UN human rights experts on Tuesday took Cambodia to task over the slum clearance.

ABC Asia Pacific TV / Radio Australia