The fires were set "as fast as they could drive from one location to the next," Bibb County Chief Deputy Sheriff Kenneth Weems said of the cluster of blazes, all near U.S. 82 and Highway 139.
Most of the churches were Baptist and all were in Bibb County, about 25 miles south of Birmingham.
Another Baptist church in nearby Chilton County also burned on Thursday, but it had been undergoing construction, which could have been a source of the fire, said Ragan Ingram, a spokesman for the state insurance agency that oversees fire investigations. That church, New Harmony Holiness Baptist in Fairview, was destroyed in the fire.
No arrests had been made in the blazes by Friday morning.
In 1996, race was a factor in a series of arsons that damaged rural black churches in Alabama and elsewhere. But Ingram said the fires late Thursday and early Friday destroyed both the churches of predominantly black congregations and predominantly white congregations.
The Ashby Baptist Church in Brierfield, Rehobeth Baptist Church in Randolph and Pleasant Sabine near Centreville all burned to the ground, Weems said.
The other two churches, Old Union Baptist in Brierfield and Antioch Baptist in Antioch, were damaged.
Jim Parker, a member of the Ashby Baptist, told WBRC television in Birmingham that he understood the fire began near the pulpit and that the fires at other churches had a similar pattern.
"Our people are obviously emotionally distraught about the loss of our building," Parker tells WBRC. "However, you know, we're in the process right now making plans for Sunday and then beyond. We will rebuild.
At Old Union Baptist, the Rev. David Hand said the fire was discovered about 4:30 a.m. and extinguished before it could cause serious damage.
According to WBRC, the six churches damaged by fire overnight include Ashby Baptist Church in Brierfield, Old Union Baptist Church, also in Brierfield, Pleasant Sabine Antioch Church near Centerville, Antioch Church in Antioch, and Rehoboth Baptist Church in Randolph, all in Bibb County. The sixth church is Older Church in Chilton County.