JACKSONVILLE, Fla. -

A historic flood on the St. Marys River from heavy rainfall from Tropical Storm Debby has forced bordering counties into flood emergencies.

Those counties include Nassau and Baker in Florida and Camden and Charlton in Georgia.

Residents who live along the St. Marys River are at risk for flooding from the high water levels and the fast flowing river. Areas that do not normally flood will flood anywhere along the length of the river, emergency officials said.

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

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.

State Road 121 crossing the St. Marys River at the Florida-Georgia border remains impassable. The State Road 2 Bridge, which straddles the border, was set to close Thursday afternoon in St. George, Ga., because the river was cresting, though officials were doing what they could to keep it open.

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

About 100 people have left their homes along the river in Baker County, though some refused. The Red Cross has shelters open at Macclenny Elementary School on Wildkitten Drive, and New Life Baptist Church, 1058 Wheeler Street, in St. George.

Extreme flooding may occur at Flea Hill and Kings Ferry in Camden County through Friday night. Overland flooding will extend to and possibly connect with the Satilla River to the north and west of State Road 110 near the intersection of Highway 110 and Highway 40 near the Camden-Charlton county line, officials said.

Residents and those with interests along the river, as well as any neighborhoods near the river that are prone to flooding, are encouraged to take immediate actions to protect threatened property. Keep children away from flooded areas. Do not drive vehicles through flooded areas.

Sandbags are available for residents who live along the St. Marys River in Camden and Nassau counties. In Camden, the sandbags may be picked up at the Facilities Management office located at 1144 Godley Avenue in Woodbine. Nassau County has also set up two locations to hand out sandbags: 3613 Bailey Road in Fernandina Beach and 45377 Mickler Street in Callahan.

Residents should closely monitor the situation with a heightened level of urgency and not wait until the last minute to evacuate. If you find yourself in immediate danger, call 911.