The cessation of hostilities was due to start at noon (4 a.m. ET), it said.
The news agency said the ceasefire was "extendable" as long as Houthi militias and forces loyal to them abide by it.
The aim is to allow the entry of humanitarian aid to besieged areas, the news agency said, particularly Taiz City. But coalition forces will respond to any military movements from the opposing side, it said.
The truce is a response to efforts by the United Nations and the international community to bring peace to Yemen, the Saudi Press Agency said.
Ismail Ould Cheikh Ahmed, UN special envoy for Yemen, welcomed the development in a statement Saturday, saying it "is necessary to avoid further bloodshed and destruction and should allow for the expanded delivery of humanitarian assistance."
He urged all parties in Yemen and the region, as well as the international community, to respect the ceasefire "and to ensure that it leads to a permanent and lasting end to the conflict."
He said both sides in the conflict had committed to sending representatives to talks in Saudi Arabia aimed at supporting the "cessation of hostilities" under terms agreed to in April.
Ceasefires have been declared before in Yemen, but each time conflict has resumed.
About 10,000 Yemenis have died and millions are in need of aid in a 20-month conflict that has been dubbed the "forgotten war
," because it has occurred in the shadows of the Syrian conflict.
Kerry meets with Houthis
US Secretary of State John Kerry met with a Houthi delegation in Muscat, Oman, in a push to make progress on resolving the conflict, State Department spokeswoman Elizabeth Trudeau told reporters earlier this week.
The Houthis, who are backed by Iran, indicated a willingness to abide by the terms of the cessation of hostilities established in April, she said, provided other parties also stick to it.
"We understand the Saudi-led coalition has also expressed a willingness to return to the cessation. Additionally, the Houthis accepted the UN-drafted road map as a basis for negotiations to end the conflict to work for the establishment of a new national unity government," she said.
The Saudi Press Agency reported that the truce was declared on the basis of Saudi King Salman receiving a message from Yemeni President Abdu Rabu Mansour Hadi.
Millions at risk of starvation
The war in Yemen began in early 2015 when Houthi rebels -- a minority Shia group from the north of the country -- drove out the US-backed government and took over the capital, Sanaa.
The country has become a proxy battleground between Saudi Arabia and Iran.
A Saudi-led coalition, made up of several Arab countries, began a military campaign in March 2015 aimed at restoring the Yemeni government and preventing the Houthis and forces loyal to deposed President Ali Abdullah Saleh from taking power.
In August, peace talks failed, prompting an increase in airstrikes in the weeks that followed.
Last month, the World Food Programme warned that millions were at risk of starvation
in Yemen, saying "an entire generation could be crippled by hunger."
UN humanitarian chief Stephen O'Brien also gave a strongly worded statement to the UN Security Council in late October urging an immediate cessation of hostilities to save a generation of Yemenis from "humanitarian catastrophe."