The National Weather Service issued a flash flood emergency for Fayette and Shelby Counties in Tennessee after radar estimates indicated that 4 to 6 inches of rain had fallen across the area during a three hour span early Thursday morning.

A slow moving cold front brought showers and thunderstorms to the region early on Thursday.

These thunderstorms continued to develop over the same areas around Memphis, resulting in very heavy rain. Rainfall rates of one to two inches per hour were seen just north of Memphis.

(MORE: Homes Flooded, Cars Stranded in Memphis, Tenn.)

Homes to the north of the city were inundated, prompting the Memphis Fire Department to send boats to carry out rescues for residents trapped there. According to the Commercial Appeal, boat rescues began at 7:30 a.m. and were completed by 8:50. It's not immediately clear how many rescues were carried out, but no injuries were reported.

As of Thursday evening, Shelby County reported 40 people were in shelters. The forecast says more rain is possible through Friday before drying out by Saturday.