Markets have tumbled after trading halted in parts of North Dakota, Iowa, and South Dakota, all of which are among the worst hit by the North Dakota wildfires.
The firefighting operations were halted in South Dakota and Iowa early Wednesday and reopened in the state early Thursday.
North Dakota Governor Dennis Daugaard tweeted that there would be “no trading” in the states.
Daugaard said the state would likely have to shut down some schools and businesses to allow firefighters to work in the area.
The North Dakota National Guard said it was responding to the fires on the north side of the state’s Big Sioux Reservation.
The fire, which has now burned about 6,700 square kilometres (2,800 square miles), has been burning for a week.