UK aid agencies and celebrities have launched a television and radio appeal to raise millions of pounds for those facing starvation in Niger.
Hundreds of thousands of children are at risk from hunger and malnutrition.
A locust plague followed by drought blighted Niger and neighbouring west African countries.
"We need the public to donate whatever they can to help us save lives," said the Disasters Emergency Committee (DEC), which will run the appeal.
According to the Red Cross, almost eight million people are at risk of hunger not only in Niger, but also in neighbouring countries.
Those starving need at least £8m to help their plight, according to the DEC.
Short films fronted by actor Dougray Scott and presenter Jeremy Vine were shown on the BBC and ITV for the first time on Tuesday to spearhead the Niger Crisis Appeal.
And posters advertising the campaign have been unveiled in charity shops and high street banks in a bid to draw attention to the cause.
In Mali, some 1.1 million people will need food aid this year and in northern Burkina Faso 500,000 people need help.
Niger - the world's second-poorest nation - has been ruined by decades of chronic poverty.
Before the current crisis, 40% of children were malnourished and the north-west African country had the second highest global mortality rate among children under five.
Millions are struggling to deal with the effects of a persistent lack of food, safe water and basic healthcare, say the charities.
The appeal funds will go to relief programmes, including the purchase and distribution of food, animal fodder, seeds and medicines.
Celebrities Myleene Klass and Melinda Messenger were among 140 people who answered phones to take donations at a call centre set up in London on Tuesday.
Klass, 26, described news footage of the famine as "absolutely devastating".
"When we are sitting at home having our dinner and we see the images of a mother walking for two days to get her child some food, it's very humbling.
"It puts things in perspective."
Messenger, 34, said: "Particularly being a mum, to see children and babies in that situation tore my heart out."
DEC chief executive Brendan Gormley said there were about 6,000 phone lines and 36,000 calls had been received just before the TV appeal was broadcast.
"This is an actual emergency facing hundreds of thousands of people. They need help now.
"We need the public to donate whatever they can today to help us save lives."
Donations to the DEC Niger Crisis Appeal can be made at www.dec.org.uk, by phoning the Disasters Emergency Committee on 0870 60 60 900, or by posting cheques to DEC Niger Crisis Appeal, PO Box 999, EC3A 3AA.
From Tuesday donations can be made by going into any high street post office or bank.