SIKESTON, Mo. — The Army Corps of Engineers planned to blow a nearly 2-mile-wide hole in an earthen levee late Monday, unleashing a muddy torrent into empty farm fields in a desperate bid to save an Illinois town from rising floodwaters.

Engineers announced their intention to carry out the blast after spending hours pumping liquid explosives into the Birds Point levee near tiny Cairo, Ill. The first explosion was to happen not long after nightfall.

But doubts persisted about whether breaking open the levee would provide the relief needed. How much water would the blast really divert from the Mississippi River? And will authorities have to do the same thing at other trouble spots downstream?

Time was running short to find answers. Five more inches of rain fell overnight, further straining the floodwall protecting tiny Cairo, Ill. And still more was in the forecast.

The seemingly endless rain has overwhelmed rivers and strained levees, including one protecting Cairo, at the confluence of the Ohio and Mississippi rivers.

The Ohio River at Cairo had climbed to more than 61 feet as of Monday, a day after eclipsing the 1937 record of 59.5 feet.

The river was expected to crest late Wednesday or early Thursday at 63 feet — just a foot below the level that Cairo’s floodwall is built to hold back — before starting a slow decline by Friday.

The high water has raised concerns about the strain on the floodwalls in Cairo and other cities. The agency has been weighing for days whether to blow open the Birds Point levee, which would inundate 130,000 acres of Missouri farmland.

Engineers believe sacrificing the levee could reduce the water levels at Cairo by about 4 feet in less than two days. Meteorologist Beverly Poole of the National Weather Service put the figure closer to 5 feet.

“These are uncharted territories, but it would be very fast,” she said.

Carlin Bennett, the presiding Mississippi County commissioner, said he was told a 10- to 15-foot wall of water would come pouring through the breach.

“Tell me what that’s going to do to this area?” he said. “It’s a mini-tsunami.”

Crews planned to begin the detonation sometime between 9 p.m. Monday and midnight. The first blast was expected to be the most intense. Two more series of explosions were scheduled, with the second one occurring sometime after 1 a.m. Tuesday and the third going off around midday.

The demolition was expected to cover about 11,000 feet of the levee.