UPDATE 3-'Monster' Hurricane Michael strengthens on its way to Florida

Hurricane Michael strengthened to a Category 2 storm on Tuesday as it headed for the Florida Panhandle, where residents were ordered to get out of harm's way ahead of life-threatening waves, winds and rains.

Tens of thousands of people were told to evacuate the coastal areas in nine counties as the storm moved over the Gulf of Mexico, carrying winds of 100 miles per hour (155 km per hour) and disrupting oil production.

Michael could grow to a Category 3 storm on the five-step Saffir-Simpson scale before it makes landfall on Wednesday, forecasters said, potentially the most powerful storm to strike the Panhandle in at least a decade.

"Hurricane Michael is a monster storm and it keeps getting more dangerous. We're 12 hours away from seeing impacts," Florida Governor Rick Scott told a news conference on Tuesday. "The time to prepare is now."

He warned of potentially deadly impacts from a storm surge that could be as much as 12 feet (3.7 meters) over normal seawater levels, and winds that could rise to 110 mph (177 kph).

People in potentially affected areas should not take any chances against such a large storm surge, Scott said. "No one's going to survive," such a wall of water, he added.

As Michael moved over open water, energy companies halted nearly one-fifth of Gulf of Mexico oil production and evacuated personnel from 10 platforms on Monday.

The Gulf of Mexico produces 17 per cent of daily U.S. crude oil output and 5 per cent of daily natural gas output, according to the U.S. Energy Information Administration.

The storm was forecast to make landfall somewhere over the Florida Panhandle or Florida Big Bend area on Wednesday, the National Hurricane Center forecast. The centre warned residents along more than 300 miles (480 km) of coastline, from the Alabama/Florida border to the Suwannee River in Florida, to brace for hurricane conditions.

As much as 1 foot (30 cm) of rain was also forecast across Florida, Georgia and South Carolina, the NHC said.

CLOSURES AND LINES FOR GAS

Scott declared a state of emergency in 35 counties along the Panhandle and Florida's Big Bend regions. About 1,250 National Guard soldiers were assisting and more than 4,000 troops were placed on standby.

State offices, schools and universities were closed through the end of the week in Panhandle counties. Lines at gasoline stations grew as people left. Those who stayed emptied grocery store shelves of water and other supplies.

In neighbouring Alabama, Governor Kay Ivey declared an emergency for the entire state on Monday, anticipating wind damage, heavy rains and power outages.

Hurricane Michael would be the first major hurricane to hit the Panhandle since Hurricane Dennis in 2005, which made landfall near Pensacola, according to hurricane centre data.

Torrential downpours and flash flooding from Michael over the weekend caused 13 deaths in Central America.

After striking Florida, Michael is forecast to move up the East Coast on Wednesday and Thursday through the Carolinas, which are still recovering from Hurricane Florence.