BRISBANE - The global financial crisis that led to the first G-20 summit in 2008 is mostly over, but the grouping of the world's largest economies must not lose focus of its core mandate of getting global growth back on track, Prime Minister Lee Hsien Loong said on Sunday.

In closing remarks at the two-day Group of 20 (G-20) summit, he reminded world leaders that "we have not solved all the structural issues" that led to the financial crisis in the first place.

"The panic has subsided but given time, the problems can come back in a slightly different form to hurt us," PM Lee cautioned at a working lunch towards the end of the Brisbane meetings, in which issues like climate change and the Ebola outbreak edged in on host Australia's growth-focused agenda.

Each country must, therefore, undertake structural reforms and work together to improve trade freedoms, multilateral institutions and infrastructure investments, PM Lee added.

"We have to deal with our own domestic constituencies to build support for reforms, be it in trade and labour markets, or rules for domestic and financial institutions," he said. "Without national reforms, no amount of global cooperation or consensus will succeed in boosting growth."

G-20 leaders on Sunday signed off on about 800 measures to grow their combined economic output by an extra 2.1 per cent - or about US$2 trillion (S$2.6 trillion) - by 2018. They also agreed to create a Global Infrastructure Hub in Sydney, as part of an initiative to better match infrastructure projects with private investors, and to push forward with the stalled Doha free trade talks.

Apart from promoting trade and infrastructure, progress must be made on reforming the International Monetary Fund (IMF) to give emerging countries more heft, PM Lee said. He joined the G-20 leaders in urging the United States to ratify the IMF reforms.

Focusing on all these economic issues will leave global leaders "a bit of energy and time to discuss other issues", he added.