Abidjan - Security forces loyal to Laurent Gbagbo, Cote d'Ivoire's disputed president, have shot dead at least six women at a demonstration in support of his rival, Alassane Ouattara, witnesses said.

Thursday's shooting took place after several hundred women gathered in the Abobo neighbourhood of Abidjan, the country's commercial capital, shouting "Gbagbo, get out!" and "Alassane for president", a resident told the AFP news agency.

Mohamed Dosso, an assistant to the mayor of Abobo, said an armoured personnel carrier and several pickup vehicles showed up as the women were protesting and opened fire.

Sirah Drane, 41, who helped organise the march, said she was holding a megaphone, preparing to address the large crowd, when she saw tanks arriving.

"There were thousands of women," she said. "And we said to ourselves, 'They won't shoot at women.' ... I heard a boom. They started spraying us. ... I tried to run and fell down. The others trampled me. Opening fire on unarmed women? It's inconceivable."

The attack prompted an immediate rebuke from the US, which like most governments has urged Gbagbo to step down and has recognised his rival as the country's legitimate president.

"The moral bankruptcy of Laurent Gbagbo is evident as his security forces killed women protesters," PJ Crowley, the US state department spokesman, said in a Twitter message.

The UN has said more than 200,000 people have fled Abobo amid days of heavy street fighting between police loyal to Gbagbo and rebel soldiers allied with Ouattara.

The UN's refugee agency has expressed alarm about the dire conditions facing people trying to get out of the area, citing "reports of many dead bodies, buses burned and shops looted, and of young militiamen attacking people inside their homes".

Gbagbo has cut power and water supplies to the country's north, under the control of rebels, which might fuel a humanitarian crisis, a UN spokesperson in Cote d'Ivoire has confirmed.