From the BBC
Speaking at a conference in the Bangladeshi capital Dhaka, he said efforts must be made to create a $100bn (£63bn) Green Climate Fund.
The global economic crisis should not deter such efforts, he added.
The event was organised by the Climate Vulnerable Forum (CVF), which connects countries affected by extreme weather.
Mr Ban said governments meeting in Durban later this month for UN climate talks must make concerted efforts to help countries likely to bear the brunt of climate change.
“Governments must find ways – now – to mobilise resources up to the $100bn per annum as pledged. The fund needs to be launched in Durban,” he said.
“An empty shell is not sufficient. Even in this difficult time we cannot afford the delay.”
He said taking action against climate change was not a luxury.
“It is an imperative which we have to do in all the circumstances. We cannot ask the poorest and the most vulnerable to share the brunt of this impact.”
Mr Ban also said he expected the Durban meeting to find a compromise on the Kyoto Protocol, to reach a broader comprehensive climate agreement in the future.
The Kyoto Protocol, adopted in 1997, mandated relatively modest reductions of emissions of greenhouse gases by industrialised nations.
The CVF was formed in 2009 by countries including the Maldives, Bangladesh and other small island states at risk from cyclones and rising sea levels.
Experts say a 1m rise in sea levels would flood more than 15% of Bangladesh and create millions of climate refugees.
Bangladeshi Prime Minister Sheikh Hasina said the response from the world community so far had been slow and inadequate.
“Climate change has been seriously affecting us. We are bearing the brunt of the damage though we made negligible or no contribution to the menace. This constitutes a serious injustice and must be acknowledged by the global community,” Ms Hasina said.
Members of the forum argue that their own efforts to cut carbon emissions will also put moral pressure on richer nations.