Weather agencies including Australia's must step up co-operation to close a "widening gap in capacity" with developing nations, with the urgency of action increasing as the planet heats up, David Grimes, president of the World Meteorological Organisation (WMO), says.

The increasing frequency of severe heatwaves, heavy rain events and droughts means it is even more important richer nations such as Australia shared their expertise in forecasting and early warning.

"It's becoming more urgent. The reality in the developing world is they lack a lot of tools," said Mr Grimes, ahead of a two-day Australian Meteorological and Oceanographic Society symposium in Melbourne starting on Tuesday. "You've got countries that can barely keep their monitoring systems functioning."

The potential benefits of early warning have been on show this month as heavy monsoonal rains hit many parts of South Asia, while a deluge near Freetown in Sierra Leone triggered a landslide that killed more than 500 people.