The UN has launched a $500m (£288m) emergency fund to speed up the handout of money for humanitarian disasters.
The UN says 11 million people in the Horn of Africa face starvation
The initiative, put forward by the UK, was launched by Secretary General Kofi Annan in New York.
Mr Annan wants cash from the fund to immediately help millions in the Horn of Africa threatened with starvation.
But worldwide responses to the fund have been muted - with only a quarter of the amount needed raised so far, of which a third has come from the UK.
UK International Development Secretary Hilary Benn described the world's reaction to disasters as similar to that of a fire brigade having to go round with a collecting tin to raise funds before it can put out fires.
"Until today, every time disaster strikes, the UN has had to appeal to the world for donations. This takes too long and costs lives.
"Now, with this single source of rapid funding, there should be less forgotten crises and less focus on passing around the begging bowl when crises do strike," he said.
Lack of response
The Swedish president of the General Assembly, Jan Eliasson, said the initiative's success would "depend on the level of funding it receives".
Developing nations such as Pakistan, India and Egypt have pledged money to the fund, while richer countries like Germany and Japan had not, according to Oxfam International.
"Governments must pledge to the fund now, before the next emergency occurs," Oxfam's policy advisor Greg Puley said.
Some question whether on-going crises such as Darfur should qualify
The fund will be managed by the UN emergency relief coordinator Jan Egeland in consultation with humanitarian agencies and the relevant humanitarian co-ordinators.
Mr Egeland told the BBC he hoped it would "inject some equity into the system".
The "most neglected, most forgotten" emergencies such as Central African Republic, Ivory Coast or Chad would also receive money from the fund as well as sudden disasters.
"These are places where there are great needs and where we usually have around one third or less of what we've asked for," he said.
The central fund has so far raised just under $200m (£115m) from 23 member states. Mr Egeland said they needed an extra $450m.
But some aid agencies outside the UN system who are often the first to respond to disasters are concerned that they could lose out financially.
Another concern is who will decide what constitutes an emergency under the terms of the fund.
The BBC's developing world correspondent David Loyn says an ongoing crisis such as the Sudanese region of Darfur is likely to need much steadier funding than could be provided by the emergency scheme.