Fighting between dissident troops and those loyal to embattled President Ali Abdullah Saleh resumed at dawn after a brief lull overnight and raged through the day before receding in the evening, medics and witnesses said.
The defence ministry said early evening that Vice President Abdrabuh Mansur Hadi had given "strict orders for a rapid ceasefire in the capital and that government forces were obeying."
An opposition official said the dissident troops had been observing a ceasefire since noon to "foil the plans of the band that wants a military escalation."
EU foreign policy chief Catherine Ashton had earlier urged an immediate end to the bloodshed and pressed Saleh to agree to a transfer of power in the face of the mass protests that have rocked his regime since mid-January.
Republican Guard troops, commanded by Saleh's son, Ahmed, shelled posts held by troops of the First Armoured Brigade loyal to dissident General Ali Mohsen al-Ahmar around Change Square, epicentre of the protests, witnesses said.
Change Square was targeted by mortar rounds and anti-aircraft fire, with one witness describing it as the "heaviest shelling" yet and saying it "lit the sky over the square."