(Recasts, adds details)
By Tansa Musa
YAOUNDE, Feb 27 (Reuters) - Anti-government riots paralysed Cameroon's capital and main port city on Wednesday as popular anger exploded over high fuel and food prices and a bid by President Paul Biya to extend his 25-year rule.
The unrest -- the worst in more than 15 years in the central African oil producer -- has killed at least six people since it broke out at the weekend in the port of Douala, a major shipping hub on Africa's west coast.
It spread on Wednesday to the inland capital Yaounde after sweeping through western towns in the last four days.
Riot police fired teargas at protesters in both cities, sometimes using helicopters to drop gas canisters from the air.
State radio appealed for calm, saying the government had agreed with union leaders to make small cuts in gasoline and fuel prices, one of the key demands of the protesters. But people expressed outrage at the small size of the reductions.
In Yaounde, bands of stone-throwing youths blocked streets with barricades of burning tyres and timber. Businesses and shops closed and parents rushed to fetch their children from schools. Some vehicles left in streets were smashed and torched.
Some protesters chanted slogans against Biya, whose announcement last month that he might seek changes in the constitution to prolong his mandate has angered many opposition supporters. "Biya has gone too far, he must go," shouted one demonstrator in Yaounde.
Others chanted: "We're fed up".
In the commercial capital of Douala, a police helicopter dropped tear gas on hundreds of protesters who marched to demand bigger cuts in fuel and food prices. As the marchers scattered in panic on Wouri Bridge, some fell into the river.
Witnesses saw police arrest dozens of protesters, taking them away in trucks. Some were beaten with rifle butts, the witnesses said. Anti-government protests were also reported in Bamenda in the northwest.
Cameroon is the world's fourth largest cocoa producer but no details were immediately available on disruption to shipments.
EXPENSIVE OIL HIKES PRICES
Cameroon's government and union leaders reached an agreement late on Tuesday to end a taxi drivers' strike which had triggered the rioting and widespread looting in Douala -- a hotbed of opposition against Biya -- and other towns.
The government agreed to cut the price of a litre of gasoline to 594 CFA francs ($1.36) from 600. Similar small reductions were agreed for other fuel products like kerosene.
The riots followed similar protests against the high cost of living in other West African countries after soaring oil prices pushed up prices for energy products and basic foodstuffs.
Biya announced eight weeks ago he might change the constitution to stay in power when his term ends in 2011. Critics say Biya, 75, could use his party's majority in parliament to make the constitutional modifications.
The U.S. embassy in Cameroon advised its citizens to avoid travel inside the country. "Roadblocks have been erected without notice by both demonstrators and petty criminals on many of the major thoroughfares of Cameroon," it said in a message posted on the embassy Website.
"Food, fuel and water are increasingly scarce, not only in Douala but in other cities where expectation of shortage has sparked a run on gasoline," it added. (Additional reporting by Talla Ruben in Doula; Writing by Pascal Fletcher)