Raids target Houthi strongholds across country while ground fighting reported in the southern city of Aden.
The air strikes early on Saturday hit targets in the city of Hudaydah on the Red Sea Coast, the Houthi stronghold of Saada in the north, and military installations in and around the capital Sanaa.
The air strikes also struck the base of Yemen's former President Ali Abdullah Saleh, who ruled the country for more than 30 years. Saleh is believed to have fled to Sanhan, near the capital.
The air strikes come amid reports of ground fighting between forces loyal to President Abd-Rabbu Mansour Hadi and the Houthi rebels in the southern port of Aden.
The spokesman for the Arab coalition bombing Houthi targets in Yemen, Brigadier General Ahmed Asiri, said that Saudi Arabia and its allies will do whatever it takes to stop Yemen's second largest city from falling to the Shia rebels.
Asiri said in Riyadh on Friday that the coalition's "main objective [is] to protect the government in Aden".
Asiri's comments came as a US defence official told Al Jazeera that US forces had rescued two Saudi airmen on Thursday who had ejected from their F-15 fighter jets over the Gulf of Aden. The official said a HH-60 helicopter from Djibouti recovered the Saudi airmen in international waters.
The defence official said the rescue took place at Saudi Arabia's request and a statement issued by the White House said that Saudi's King Salman had thanked US President Barack Obama in a phone call.
Saudi Arabia's state news agency reported that the fighter plane had been "stricken by a technical fault".
Asiri's remarks came as warnings were raised that a humanitarian disaster could unfold should the conflict escalate.
Bashrahil Hesham Bashrahil, a journalist based in Aden, said civilians were scared and leaving the city with the once busy streets now eerily quiet.
"The markets are closed, businesses are closed and there is a real shortage of food," Bashrahil told Al Jazeera.
"Banks have been shut since Thursday and will not reopen until the security situation has been addressed.
"While power supplies have not yet been effected there is a real sense of fear should the fighting worsen," he said. "Hospitals are struggling to cope with the number of injured and are appealing for blood donations."
Houthis and Hadi loyalists have been clashing on the outskirts of the city in the last few days, leaving many casualties.
Aden is believed to harbour dozens of army defectors and Houthi fighters.
Hadi left Aden on Thursday under Saudi protection. After a stop in Riyadh, he arrived on Friday in the Egyptian city of Sharm el-Sheikh where he is to attend an Arab Summit focusing on the military intervention in Yemen.
Saudi Arabia has been bombing Houthi targets since Thursday in what they call Operation Decisive Storm, after assembling a coalition of more than 10 countries, five of them members of the six-nation Gulf Cooperation Council.
The Houthi-run health ministry said on Friday that 39 civilians had been killed. Amnesty International said six children were among those killed in Sanaa on Thursday.
Egyptian and Saudi warships have been deployed to the strategic Bab al-Mandab strait, a key trade and oil route separating the Arabian Peninsula from east Africa.
An Egyptian military official told the AP news agency that two destroyers and two other vessels were at the strait.