Officials in Ethiopia hope to plant 200 million trees in a single day in what they hope will be a world record.
Prime Minister Abiy Ahmed is leading the project which aims to counter the effects of deforestation and climate change in the drought-prone country.
Some public offices have been shut down to allow civil servants to take part.
The UN says Ethiopia’s forest coverage declined from 35% of total land in the early 20th Century to a little above 4% in the 2000s.
Mr Abiy launched the tree-planting exercise as part of his Green Legacy Initiative, which is taking part in 1,000 sites across the country.
The aim is to plant a total of four billion trees.
The BBC’s Kalkidan Yibeltal in Addis Ababa says that for days, promotional videos have run on state media urging the public to plant and care for trees.
The current World Record for planting trees in a single day is held by India, which used 800,000 volunteers to plant more than 50 million trees in 2016.
Ethiopia’s Minister of Innovation and Technology Getahun Mekuria has been tweeting about the progress:
Critics of Mr Abiy say he is using the campaign to distract the public from the challenges his government is facing, including ethnic conflicts which have forced some 2.5 million people from their homes.