Twenty-five homes have been evacuated in Big Stone City after a semi-tanker filled with anhydrous ammonia rolled over and started leaking dangerous chemicals.

Authorities say It happened on Highway 12 on the South Dakota and Minnesota border between Ortonville and Big Stone City. Grant County Sheriff Mike McKernan says officials have evacuated around 75 people in eastern Big Stone City as a precaution.

One witness who was traveling from Ortonville back into South Dakota had to take a detour because officials have blocked off Highway 12.

"I went through Ortonville and went back out onto the other road and there was another police officer who was saying that no one is allowed to come into South Dakota right now. He said it's going to be a very long time and you'll have to take an alternative route," Jena Schulte said. 

The semi tipped over after a van heading east on Highway 12 crossed the center line and hit the tanker. The collision happened just before eight Wednesday night. The driver of the van was taken to the hospital with unknown injuries, and the semi driver has minor injuries.

Local fire departments are spraying down the small ammonia vapor leaking from the tanker, and are expected to be on the scene until early Thursday morning.

We'll have more updates on KELOLAND.com and on KELOLAND This Morning starting at 5 a.m.