A seven-day ceasefire went into effect on Tuesday between the Saudi-backed Yemeni government forces and the Shia Houthi rebel group across the country.
The renewable ceasefire coincides with the kick-off of UN-sponsored peace talks in Switzerland between the two warring sides.
"A ceasefire has just begun at 12.00 p.m. (local time) for seven days to halt all military operations across Yemen and allow the delivery of humanitarian aid to reach people," a government official told Xinhua news agency.
"It also includes stopping all airstikes by the Saudi-led Arab coalition against Houthi-controlled positions in Yemen," the official said.
However, military sources said sporadic armed confrontations continued between Houthi rebels and government loyalists in Marib province 50 minutes after the beginning of the truce.
Houthis also fired five shells on sites of pro-government forces in Yemen's third largest city of Taiz, causing casualties among civilians in the area, according to local residents.
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A tribal chief said: "Houthi gunmen breached the ceasefire just 30 minutes after its commencement and clashes are taking place near the southern province of Lahj."
Yemeni President Abd Rabbu Mansour Hadi had proposed the truce last week and announced that it would be extended if the Houthis and their allies lift the siege on Taiz, free detainees and end military actions.
More than 6,000 people, majority of them civilians, have been killed in Yemen since March in ground battles and airstrikes.