(CNN)More neighborhoods in Jackson, Mississippi were starting to flood Saturday as the swollen Pearl River may soon reach its highest point in decades, city officials said.
Pearl River is expected to crest Sunday and lead to 'historic' flood in Mississippi
Authorities urged people in mandatory evacuation zones in Mississippi's capital to leave their homes or ask for help evacuating.
"Please, please get out before dark tonight," Gov. Tate Reeves said at a news conference, addressing hundreds of people whom officials have asked to evacuate near the river in the Jackson area.
As of Saturday night, the Pearl River, already moderately flooding some neighborhoods around northeast Jackson, had risen to nearly 36 feet and nearly 8 feet above flood stage, the National Weather Service said.
The river is expected to crest at 38 feet early Sunday, city officials said.
At 38 feet, "a large number of homes are flooded in northeast Jackson," water will enter some buildings downtown and roads will become impassable, city officials and the weather service said.
Some 2,400 homes and other buildings are at risk of being flooded, Reeves said.
Reeves declared a state of emergency "to deploy the necessary resources to take care of Mississippians that are impacted," he said.
"Do not wait till until water envelops your home or blocks the road so that you cannot get out," said Mississippi Emergency Management Agency Director Gregory Michel at the news conference in Pearl, near Jackson.
"When you take risks like this, it puts first responders, emergency responders at additional risks to come in and get you out of a home after it's been flooded."
If the river crests at 38 feet, it would be the third-highest crest there on record, the weather service says.
"This is a historic, unprecedented flood," Reeves tweeted on Saturday.
The record is 43.3 feet, set in April 1979. The next highest was 39.6 feet, set in May 1983.
Evacuations were ordered Friday for parts of Jackson, and police officers were visiting affected homes to alert the residents, Mayor Chokwe Lumumba said.
The city invited residents to pick up sandbags -- to use as water barriers at their homes -- from a lot where the supplies had been delivered. More than 96,000 sandbags had been delivered to Hinds County, the governor said.
In northeastern Jackson, the Pearl River flooded yards and roads in the Cypress Trail area on Thursday, CNN affiliate WAPT reported. Pickup trucks and ATVs could make it through the flooded roads, but cars were turning around.
Most of Arsheka Davis-Jackson's yard was filled with water.
"I am terrified," she told WAPT. "I have a business I'm running inside my home. I work from my home. So this is going to mess up a lot of things."