Britain's Prime Minister Gordon Brown is due to host a summit on Saturday outside London with some 20 world leaders on climate change, economy and global poverty.

Chilean President Michelle Bachelet, Australian Prime Minister Kevin Rudd, Liberian President Ellen Johnson-Sirleaf and former US President Bill Clinton are among those due to attend the two-day conference and summit at The Grove hotel, in Watford.

Speaking on Friday at the Progressive Governance conference, a prelude to the summit, Brown talked about what he called "probably the first truly global financial crisis of the modern world."

"It is underpinned by probably the biggest restructuring of the world economy that has ever taken place since the industrial revolution and the biggest shift of power to Asia that we've seen in these centuries."

Brown also pointed out that financial rules have also experienced great changes.

"The national rules and the national regulations we adopt for economic matters bear no relationship to the global nature of capital flows and the global nature of international business organization that exists at the moment, so we will have to reform our global financial institutions."

New Zealand Prime Minister Helen Clark also addressed the conference, focusing on climate change.

"We are having to take very tough decisions in the first world on how we deal with greenhouse gas emissions and there are political and economic costs involved in that."

Summit participants are expected to hold round-table discussions and try to issue a short joint statement after the summit.