JACKSONVILLE, Fla. -

Baker County Sheriff's Office expands its mandatory evacuation for people living along the St. Marys River, its tributaries and its flood basin.

The National Weather Service in Jacksonville said the river would continue to rise for the next 24 hours above an already historic crest. It's expected to affect portions of Baker and Nassau counties in Florida and Charlton and Camden counties in Georgia.

"The notice said it was extreme, could be extreme danger for people to stay on the river and not retreat from their homes.," Baker County Sheriff Joey Dobson said. "We certainly don't want to make them leave but we think it's in their best interest and the safety of their families and themselves to leave the area until this water recedes."

The St. Marys River near Macclenny was at 24.3 feet at 6:45 a.m. Thursday -- 12 feet above flood stage and surpassing the all-time 23.2-foot crest of September 1964.  The river is expected to slowly recede after Thursday, but remain in major stage through Sunday.

"It will continue to rise. This is the highest elevation of the river since 1947. That tells us a lot and we've seen it real high before," Sheriff Dobson said. "This rain we've received this time is a larger amount than we've ever had before."

State Road 121 crossing the St. Marys River at the Florida-Georgia border remains impassable. The Main Bridge in St. George, Ga., was set to close Thursday afternoon because the river was cresting.

Residents who need assistance with evacuation are asked to call the Sheriff's Office at 904-259-2861.

The Red Cross has shelters open at Macclenny Elementary School on Wildkitten Drive and New Life Baptist Church, 1058 Wheeler Street, in St. George.

The Sheriff's Office says about 100 people left their homes north of Macclenny after an initial evacuation order was issued Tuesday night, but a few refused to leave.

Out with a Florida Fish and Wildlife officer patrolling the properties by boat Wednesday, Channel 4's Jason Law ask those staying put why they wouldn't leave.

"Protecting the property," was Jimmy Jesseman's answer.

FWC officer Bret Gill said those staying probably won't have electricity for the next week.

"Until it starts going down," Gill said. "It's still rising."

Joe Orfield did evacuate when asked, but was out in a canoe Wednesday checking on his property.

"I'm OK right now, as long as it doesn't come up another foot," Orfield said.