At least ten people protesting against the rule of Ali Abdullah Saleh, Yemen's president, have been killed by security forces and snipers after they opened fire on thousands of anti-government demonstrators in several cities across the country.
In the capital Sanaa, forces fired on a crowd of tens of thousands marching to the cabinet building.
At least six demonstrators died, and about 100 were wounded, said a doctor heading a makeshift clinic for wounded protesters at the scene.
The doctor, who wished to remain anonymous, said the number of dead could rise.
"The snipers were shooting at the people," Talal al-Hamadi, a protester, said. "People rushed and some fell over each other. There was a stampede."
In the industrial centre of Taiz, snipers killed two protesters and dozens were injured by gunfire, tear gas and bat-wielding plainclothes security men.
Demonstrators stormed the police station where gunfire which killed the second protester had come from, activist Ghazi al-Samai said.
Samai said protesters seized an officer whom they accused of shooting the fatal bullet, and handed him over to the prosecutor's office.
He said protesters then started setting tyres on fire in many streets and took control of three government buildings, including the oil ministry.
Residents said the city of 540,000 people was effectively paralysed.
"Stores are closed and the streets are completely empty of pedestrians, only protesters are around in the areas they are confronting [security forces]," Taiz resident Wajdi Abdullah said
In the Red Sea port city of Hudaida, one protester was killed when security forces opened fire after marchers tried to force their way into a government building, witnesses said.
Another protester was killed by police in Dhamar, 100km south of Sanaa, as security forces opened fire on a demonstration, medics and witnesses told the AFP news agency.
In Ibb, also south of the capital, hundreds surrounded provincial offices.
"Almost all the stores are shut in Ibb except a few selling basic food items. No one is going to work - this is unprecedented in this city," said resident Ali Noaman.
In the southern city of Aden, demonstrators set fire to tyres in the streets as the city was paralyzed by civil disobedience called by the opposition.
Similar demonstrations took place in Hadramawt.
Yemen's economy is struggling with its currency falling against the dollar, and the prices of basic necessities rapidly rising.
Residents in remote areas are also suffering severe water shortages because fuel rationing has stopped trucks from carrying water shipments they depend on.
Yemen has seen three months of daily protests, and demonstrators who are frustrated by Saleh's reluctance to relinquish his power.
In office for more than three decades, Saleh has intensified his crackdown on the protests and refused a regional mediation offer.
More than 140 people are reported to have been killed in the government crackdown on the escalating protests.