Juba - More than 170 people have been killed in fighting between rival cattle herders in central South Sudan in the past week, a lawmaker said on Tuesday.

"When it comes to those who are wounded, it is almost 200," added Dharuai Mabor Teny, a member of parliament from the Western Lakes area, some 250km northwest of the capital Juba.

It more than doubles a previous toll issued late last week, since fighting between rival factions of the Dinka people, the Rup and Pakam clans, broke out on December 6.

The government has declared the fighting a state of emergency, meaning that soldiers have been deployed after local state officials were overwhelmed.

"The state of emergency is meant to curb violence," presidential spokesperson Ateny Wek Ateny said, adding the fighters were hurling grenades and firing rockets at each other.

"Civilians are locked up in very violent communal fighting."

Local information minister of Western Lakes state Bol Machok said homes have been torched and people forced to flee.

Rival pastoralist communities in South Sudan have a long and bloody history of tit-for-tat raids in which cattle are rustled and property looted. Women are commonly raped and children abducted, adding fuel to revenge attacks.

Such attacks have worsed amidst the breakdown of society during the four-year civil war which began in December 2013.

Half the country is in need of emergency food and a third has been forced from their homes since then, according to the UN.