(CNN)Hundreds of people in Mississippi's capital have fled their homes as authorities fear the swollen Pearl River will soon unleash catastrophic flooding.
The Pearl River, which runs just east of downtown Jackson, hit its third-highest level on record Sunday morning at 36.38 feet. The river has been rising slower than expected but has reached its major flood stage and could crest at 38 feet by Monday -- its highest point in decades -- Mississippi Gov. Tate Reeves told reporters.
Several neighborhoods in northeast and downtown Jackson have been evacuated in anticipation of the flooding. After the governor declared a state of emergency on Saturday, law enforcement officers went door to door urging at least 510 people to leave their homes, Reeves said.
"We don't want to lose anyone as we respond to what is expected to be historic flood levels," the governor said.
Authorities are expecting a "historic, unprecedented flood" that the city has not seen in more than 30 years, Reeves said.
The river's highest level on record is 43.3 feet, set in April 1979. The next highest was 39.6 feet, set in May 1983.
Water is not expected to recede for days
If the river hits 38 feet a large number of homes will be flooded by 6 feet of water, roads will become impassable and residents won't be allowed to return home for days, emergency management officials said.
"We don't anticipate the situation to end any time soon. It will be days before we are out of the woods and the water starts to recede," Reeves said.
Water was nearly covering fire hydrants and mailboxes in parts of Jackson as some residents tried to evacuate. Scott Johnson, the owner of a tow truck company, took one of his trucks to a neighborhood to help residents.
"It's sad when you ride by the houses, you can see the waves," Johnson told CNN affiliate WAPT. "You barely move the truck and it's just splashing up and almost going in the houses."
The city invited residents to pick up sandbags Saturday to use as water barriers at their homes. More than 96,000 sandbags have been delivered to Hinds County, the governor said.
Parts of Jackson are already flooded
The Pearl River flooded yards and roads in the Cypress Trail area of northeastern Jackson on Thursday, 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."