Hurricane Michael slammed into the Florida coast on Wednesday as the most powerful storm to hit the southern US state in more than a century as officials warned it could wreak "unimaginable devastation."

Hurricane Michael swelled to an 'extremely dangerous' category four storm as it rumbled toward the Gulf Coast of Florida early Wednesday in what forecasters warned was an unprecedented weather event for the area.

The National Hurricane Center said the storm is now packing maximum wind gusts of 130 mph (210 kilometers), could grow even more and is expected to slam ashore later in the day along the Florida Panhandle or Big Bend area as a "life-threatening event".

Residents of northwest Florida had until early Tuesday to leave their homes ahead of Hurricane Michael, forecast to crash ashore midweek as a major Category 3 storm with "life-threatening" flash flooding possible.

A tropical storm that rapidly formed off Mexico's Yucatan Peninsula has gained new strength and could become a dangerous Category 2 hurricane with an expected midweek strike on the Gulf Coast in the Florida Panhandle, forecasts say.

Florida Gov. Rick Scott issued an order for a state of emergency for 26 counties to rush preparations in the Florida Panhandle and the Big Bend area, freeing up resources and activating 500 members of the Florida National Guard.

Preventing an extra single degree of heat could make a life-or-death difference in the next few decades for multitudes of people and ecosystems on this fast-warming planet, an international panel of scientists reported Sunday. But they provide little hope the world will rise to the challenge.

The Nobel Prize-winning Intergovernmental Panel on Climate Change issued its gloomy report at a meeting in Incheon, South Korea.

Oil giant Saudi Arabia backed down at the last minute Saturday from obstructing the adoption of a major report by the UN's climate science panel, sources told AFP.

Mosammat Rekha's older cousins grew up unable to read and write, their tiny village so frequently cut off from the nearest school by floods that would rise suddenly in their remote corner of disaster-prone Bangladesh.

Indonesia's Mount Soputan volcano on the quake-and tsunami-hit island of Sulawesi erupted Wednesday, spewing volcanic ash 4,000 meters into the air.

Severe drought, insect infestation and poor forest management have combined in recent years to kill millions of trees in the American West -- 130 million in California alone -- and provide fuel for huge wildfires.

The UN's Intergovernmental Panel on Climate Change (IPCC), which compiles comprehensive reviews of climate science, meets this week to vet and validate a report on limiting global warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit).