By late morning, floodwaters had reached the grounds of the Dow facility and were confirmed to be "comingling with on-site containment ponds," the company said in a statement, adding no employees had been hurt.
The National Weather Service (NWS) warned of "life-threatening" flooding as water levels of the Tittabawassee River in Midland, about 190km northwest of Detroit, rose to historic levels.
"Never in my whole life have we seen the dam fail," said Mark Bone, 53, a business owner chairman of the Midland County Board of Commissioners. "It flooded real bad in '86, but never like this."
Even as flooding submerged parts of Midland, the county seat and home to some 42,000 residents, under 1.5 metres of water, Bone said no injuries or deaths had been reported.
With authorities already grappling with the coronavirus pandemic, Governor Gretchen Whitmer on Wednesday called on the federal government to provide assistance.
About 10,000 people have been evacuated in Midland County, Whitmer said, after days of heavy rain caused a swollen river to overflow its banks and breach the Edenville and Sanford dams.
"Experts are describing this as a 500-year event," Whitmer told a news conference after a tour of the stricken areas. She urged residents of low-lying areas to flee to higher ground.
A spokeswoman for the Federal Energy Regulatory Commission said that as soon as it is safe, engineers will be sent to both dams to assist state and other authorities in an investigation into the cause of the breaches.
Video posted on social media showed high water lapping around buildings in downtown Midland, partly submerging bridges and roads.
President Donald Trump, already scheduled to tour a Ford Motors Co. auto plant in Michigan on Thursday, said on Twitter he had dispatched teams from the Federal Emergency Management Agency (FEMA) and the U.S. military to the flood-stricken area to lend support.