Arab League chief Nabil al-Arabi, on the eve of a regional summit in Egypt, declared his full support for the strikes against the Huthis who he said had carried out a "coup" in Yemen.
The rebels and their allies had been closing in on main southern city Aden, where President Abedrabbo Mansour Hadi has been holed up since fleeing the rebel-controlled capital Sanaa last month.
Their advance raised Saudi fears that the Shiite minority rebels would seize control of the whole of its Sunni-majority neighbour and take it into the orbit of Shiite Iran.
Huge explosions were heard in Sanaa as warplanes pounded an air base adjacent to the international airport and other locations, an AFP correspondent reported.
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At least 14 civilians were killed when seven homes near the air base were reduced to rubble, a civil defence source said.
The International Committee of the Red Cross warned that "ordinary Yemenis -- already hit hard by years of conflict -- are now enduring the effects of this escalation".
At daybreak hundreds of Sanaa families streamed out of the capital seeking the relative safety of the provinces.
In the south, residents reported hearing explosions at the huge Al-Anad air base, north of Aden, which was seized by anti-government forces yesterday.
The Saudi ambassador to the United States said the operation had begun with air strikes but that the kingdom and its allies stood ready to do "whatever it takes" to protect Hadi's government.
Ambassador Adel al-Jubeir said the kingdom had assembled a coalition of more than 10 countries, including five Gulf monarchies.
"The Royal Saudi Air Force has taken out the Huthi air defences and destroyed numerous Huthi fighter planes," a Saudi adviser said, adding that air force "has pretty much secured most of the Yemeni air space".