Sioux Falls Fire Rescue officials say they don't yet know the cause of a grass fire Tuesday evening in the northeast area of the city.

Battalion Chief Jay Tutus says the first crews to arrive around 6:30pm found a large grass fire burning south of 4100 North Harley Place.

They had the fire perimeter contained a half-hour later. No buildings were damaged, but some 20 acres were burned.

No one was injured, and crews stayed on the scene until 9:15pm to watch for embers.

The cause isn't known, but Titus reminds everyone that conditions are very dry and that grass and other vegetation can catch fire and burn quickly.