Srimad Bhagavatam Canto 05, Chapter 24, Text 07

SB 5.24.7

upavarnitam bhumer yatha-sannivesavasthanam avaner apy adhastat sapta bhu-vivara ekaikaso yojanayutantarenayama-vistarenopaklpta atalam vitalam sutalam talatalam mahatalam rasatalam patalam iti.
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
My dear King, beneath this earth are seven other planets, known as Atala, Vitala, Sutala, Talatala, Mahatala, Rasatala and Patala. I have already explained the situation of the planetary systems of earth. The width and length of the seven lower planetary systems are calculated to be exactly the same as those of earth.
Srimad Bhagavatam Canto 05, Chapter 24, Text 06
Srimad Bhagavatam Canto 05, Chapter 24, Text 08