(CNN) — The bulging Mississippi River pushed south Friday, sending hundreds of residents scrambling to get to higher ground as officials warned of a torrent of water if a major spillway is opened.

In the Arkansas town of Helena, it crested at 56.4 feet, according to the National Weather Service. Officials there issued a flood warning.

The town’s crest was higher than the previously recorded highpoint of 48.3 feet in Tiptonville, Tennessee, according to Amanda Roberts of the National Weather Service.

Its slow pace has given emergency responders more time to prepare, she said.

In Louisiana, the National Guard worked around the clock to construct a flood barrier in Morgan City.

“When you have really high levels like this, it can an add up to several weeks (for the flood waters to move through),” Roberts said

The downside, Roberts said, is that land under water could remain that way for some time.

Louisiana state and local officials braced for the possibility of major flooding in the Atchafalaya River Basin if federal authorities decide to open the Morganza spillway.

The move could lower anticipated cresting levels along the Mississippi River by up to two feet, and divert water from Baton Rouge and New Orleans, experts say.

However, state and local officials, including Louisiana Gov. Bobby Jindal, warn that opening the Morganza floodway could send a torrent down the Atchafalaya River.

Jindal urged southeastern Louisiana residents to evacuate.

“Bottom line is we still don’t have any kind of decision or notification from the U.S. Army Corps of Engineers,” Jindal told reporters Thursday. “We’re telling our people to prepare for the worst.”

Town learns 15 ft. flood is coming

“My advice is not to wait,” Jindal said.

The Corps is measuring the current flow at a river landing, and once it reaches a specified volume and velocity, the Mississippi River Commission may make a decision on the Morganza spillway.

A decision on the spillway’s opening could come between Saturday and Tuesday, officials said.

The U.S. Coast Guard said floodwaters could close the Mississippi to ships at the New Orleans port as early as Monday morning.

With the overflowing Mississippi River bearing down on New Orleans, where the water level was already at flood stage, the Army Corps of Engineers said Thursday that it was opening more bays at the Bonnet Carre spillway.

An additional 113 bays were opened, bringing the total to 223 open bays, authorities said.

The 350-bay spillway, just north of New Orleans, diverts water into Lake Pontchartrain.

The National Weather Service said that as of Thursday night, the river was at 17 feet in New Orleans, about an inch and a half above flood stage. It is expected to crest on May 23 at more than 19 feet. The New Orleans levees are built to withstand 20 feet, according to the weather service.

Upriver in Vicksburg, Mississippi, Police Chief Walter Armstrong said 600 residents had been evacuated as of Thursday night. The river is expected to crest Thursday at 57.5 feet.

Armstrong said he expected higher water Friday, with more homes affected. More than two dozen roads were closed and about 45 businesses will be closed by Friday.

Across the South and lower Midwest, floodwaters have covered about 3 million acres of farmland, eroding for many farmers what could have been a profitable year for corn, wheat, rice and cotton, officials said.

In Arkansas, the Farm Bureau estimated that damage to the state’s agriculture could top more than $500 million as more than 1 million acres of cropland are under water.

“It’s in about 10 feet of water,” Dyersburg, Tennessee, farmer Jimmy Moody said of his 440 acres of winter wheat, which was to be harvested in the coming month.

Other farmers in Mississippi, Missouri, Tennessee and Arkansas rushed to salvage what wheat they could ahead of the rising water. As for corn, farmers who were able to get into the fields during a soggy planting season in late March and April are seeing their crops in some cases under several feet of water.

Some officials said Thursday that spillover effects resulting from the flood could threaten other industries. That includes the possibility that the Waterford 3 nuclear power plant in Taft, Louisiana, could be closed, according to CNN affiliate WGNO.

The Mississippi River is expected to crest at 26.6 feet in Taft on May 23. If it reaches 27 feet, officials told WGNO, the plant’s water intake system could shut down.

Carl Rhode of Entergy told WGNO that the threat to the intake system is not a matter of nuclear safety.

However, Scott Welchel, a St. Charles Parish Emergency Operations Center official, said shutting down the plant would have a “domino effect” on local industries.

“It wold impact every industry along the river,” Welchel said. “That’s just something that isn’t easy for people to deal with, especially on a moment’s notice.”

For residents in communities along the river, the damage has been far more devastating than can be measured in dollars and cents.

Danny Moore, of Millington, Tennessee, told CNN affiliate WPTY that the recent disaster marked the second time in one year that flooding took away nearly everything he had.

Moore said that after a flood destroyed all of his furniture last year, he decided to move everything he owned into rented storage space. However, those belongings were destroyed when his storage unit was flooded several days ago.

“They say bad luck comes in threes. I hope this is the end of it,” Moore told WPTY.

The Millington resident said he lost a house to a fire in 2009. Moore said he is too preoccupied with taking care of his girlfriend, who is suffering from an infection that is damaging her liver, to look for new furniture.

“We’ll do what we’ve got to do and keey praying,” Moore said, holding back tears.