One site is near the south side of the San Joaquin River, off HWY 99 and Herndon.
Fire units arrived at the river bottom to find two separate fires burning, and there were reports of one structure impacted by the blaze.
Fresno Fire warns that there is heavy smoke in the area.
E3, E8 responded to a third vegetation fire at Tulare and HWY 41.— Fresno Fire PIO (@FresnoFire) May 10, 2020
3 grass fires are burning along Fresno highways right now, please slow down and use extreme caution driving near the fires and our crews.#fresnofire pic.twitter.com/4aKkFbPodg
Video sent by ABC30 insiders showed flames and smoke rising - visible from several miles away.
Crews are also battling another blaze off Highway 41 and McKinley and a third vegetation fire along Highway 41 and Tulare.
"Fires along the highway can adversely affect vision while driving so please use extreme caution and pay special attention and slow down when you are passing your #fresnofirefighters while they are working in these conditions," the Fresno Fire Department wrote in a Facebook post.