For the latest updates, read our Hurricane Florence live briefing here.

ATLANTA — As Hurricane Florence gained muscle over the Atlantic Ocean on Monday and sped toward the shores of North and South Carolina, government officials in both states were taking few chances, exhorting more than a million residents and tourists in coastal areas to grab their essentials, jump into their cars and head inland as part of a great coastal emptying.

The National Hurricane Center warned that the storm, which jumped to Category 4 strength on Monday with 140 mile-an-hour winds, could pummel the shore with life-threatening storm surges and soak a wide area with rains so heavy that freshwater flooding would become a major threat. It is expected to make landfall Thursday night near the North Carolina-South Carolina border.

In Myrtle Beach, S.C., Tneah Brown was listening to the warnings. At work on Monday afternoon, she weighed the many complications that would soon flow from the order issued by Gov. Henry McMaster of South Carolina, calling on people in eight counties nearest the shore to get out.

Ms. Brown knew that evacuation was necessary. She also knew it would not be easy. There was her pit bull puppy, Kaya, to think of. And her little sister. And her sister’s 3-week-old baby. And the question of whether her mother would join them as they rushed out of town by noon Tuesday, when the governor’s order takes effect.