Hurricane Helene made landfall on the Florida coast Thursday evening as a strong and potentially catastrophic Category 4 storm, bringing chaos to much of the Gulf Coast and threatening strong winds, storm surges and torrential rain.

Helene was located about 45 miles (70 km) east-southeast of Tallahassee, Florida, with maximum sustained winds of 145 mph (225 kph), the Miami-based UA National Hurricane Center said late Thursday.

The massive storm formed quickly this week and intensified as it raced across the warm waters of the Gulf, gaining speed.

Helene’s storm surge – the wall of seawater pushed ashore by hurricane-force winds – could reach heights of up to 20 feet (6.1 meters) in some places.

“This is not a survivable event for people in coastal or lowland areas,” said Jared Miller, the sheriff of Wakulla County on Florida’s coast. “Please heed the current evacuation orders as time is running out.”

States of emergency have been declared in Florida, Georgia, the Carolinas, Virginia and Alabama.

Florida Gov. Ron DeSantis had urged North Florida residents to flee before time expired and warned of flooding, road closures and power outages. Although the storm is expected to weaken once it reaches land, it is moving quickly and could spread further.

“Probably 50 miles outside the center of the storm, there will be hurricane-force winds, and then there will continue to be storm surge, particularly in the Big Bend area,” DeSantis said at a news conference Thursday evening, held at the state’s emergency operations center in Tallahassee.

John Dailey, the mayor of Tallahassee, the Florida capital that lies directly in Helene’s basin, said the hurricane could be the strongest storm to ever directly hit his city. Helene could cause “unprecedented damage the likes of which we as a community have never seen before,” Dailey told reporters on Wednesday.

Climate scientists have warned that global warming is increasing the number and strength of powerful hurricanes. While no single storm can be attributed to climate change, the new pattern of more and stronger hurricanes is being driven by the planet’s warning oceans and seas. Much of Helen’s energy came from the power it gathered over the Gulf of Mexico, where unprecedented high temperatures have been reached in recent years.

Helene is expected to be one of the largest storms to hit the region in years, Phil Klotzbach, a hurricane researcher at Colorado State University, told the Associated Press. He said since 1988, only three Gulf hurricanes have been larger than Helene predicted: Irma in 2017, Wilma in 2005 and Opal in 1995.

Parts of Florida felt the effects of the storm before it made landfall. In communities like Fort Myers Beach, Florida, water was already 2 feet above normal on Thursday. Cities like Tampa and St. Petersburg experienced storm surges of 5 feet Thursday evening.

Once the hurricane makes landfall, it is expected to move up the southeast coast from Florida to North Carolina. At least 50 million people are affected by hurricane and tropical storm warnings.

As night fell in the mountains of North Carolina, emergency responders urged residents to seek higher ground as Hurricane Helene approached land. The area was already hit by heavy rains from another storm, and forecasters predicted another 9 to 14 inches of rain could fall as the remnants of Helene move through the area Thursday evening and into Friday.

“With a storm like this, we’re seeing flooding like we’ve never seen before,” said Jimmy Brissie, emergency services director for Henderson County, south of Asheville.

As Helene passed the island, power went out in western Cuba, affecting about 160,000 customers in the province of Artemisa and another 70,000 in the neighboring province of Pinar del Río. The hurricane also forced about 800 people in the region to evacuate flood-prone areas, according to Guerrillero, a local newspaper.

The storm swept parts of Mexico’s Yucatan Peninsula on Wednesday, inundating roads and toppling trees as it passed offshore and brushed against the resort town of Cancún.

Helene is the eighth named storm of the Atlantic hurricane season, which began in June. The National Oceanic and Atmospheric Administration (NOAA) has predicted an above-average Atlantic hurricane season this year due to record-warm ocean temperatures.

Reuters and the Associated Press contributed to this report