A French armoured vehicle patrols a street in Abidjan. Presidential claimant Alassane Ouattara has declared an overnight curfew for the next three days.

Abidjan - Heavy weapons fire rang out in central Abidjan on Thursday after presidential claimant Alassane Ouattara's forces marched into Ivory Coast's main city, and his camp said incumbent Laurent Gbagbo had just hours left in power.

Residents reported heavy fighting near the state broadcaster, RTI, as well as in neighbourhoods in the south of the city after pro-Ouattara forces swiftly advanced on the lagoon-side city from several directions.

Gbagbo's elite forces took positions around the presidential palace while French soldiers were also deployed in the city to protect foreign residents. A United Nations helicopter gunship flew overhead.

Gbagbo has refused to step down since a November election that UN-certified results showed he lost to Ouattara, triggering a bloody standoff that has killed hundreds and rekindled the country's 2002-3 civil war.

“I call on you to serve your country... It is time to join your brothers in the Republican Forces,” Ouattara said in a statement aimed at encouraging members of the security forces still loyal to Gbagbo to defect.

South Africa's government said that Gbagbo's army chief of staff, General Phillippe Mangou, had sought refuge at its ambassador's residence in Abidjan, in one of the biggest blows yet to Gbagbo's grip on power.

The US government said Gbagbo had been “significantly” weakened amid defections and the disintegration of his forces.

Security sources said some of the gendarmerie had joined Ouattara's camp but others remained loyal to Gbagbo. UN troops were now also in control of Abidjan airport after pro-Gbagbo forces abandoned it, a security source and UN sources said.

Ouattara's prime minister, Guillaume Soro, said Gbagbo had only two or three hours left in power and the “game is over”.

In a dramatic four-day sweep, pro-Ouattara forces reached Abidjan after taking the key cocoa port of San Pedro and the official capital Yamoussoukro, having advanced hundreds of kilometres since the start of the week.

His government, until now blockaded in an Abidjan hotel, announced a three-day overnight curfew and ordered the closure of land, air and sea borders until further notice, according to an Interior Ministry statement.

Ivory Coast is the world's biggest cocoa producer. The power struggle had pushed prices higher, but they have tumbled since Ouattara's push began.

The capture of San Pedro, which ships half of the country's production, could kick-start the flow of beans that dried up in January due to sanctions, but diplomats said any easing of EU measures would take days. - Reuters