Balloting started at 8am on Sunday and will continue until 4pm without any break.
Meanwhile, voting was suspended at three polling stations in Titas upazila after miscreants tried to occupy the centres.
More than 25.5 million voters are expected to exercise their franchise.
In this phase, 351 chairman, 533 vice-chairman and 406 women vice-chairman candidates are contesting. But 39 chairman, 22 vice-chairman and 27 women vice-chairman contestants have already been elected unopposed.
The Election Commission announced polls schedule for 122 upazilas but all candidates in a number of them have already been elected uncontested. These upazilas do not require balloting. Polls to some other upazilas were postponed on various grounds.
This time, electronic voting machines are being used in Cox's Bazar Sadar, Patuakhali Sadar, Mymensingh Sadar, Bagerhat Sadar, Munshiganj Sadar and Feni Sadar.
A security team comprising of 14-16 members drawn from police, Ansar and VDP are guarding each polling station.
The first three phases of the upazila elections were held on March 10, 18 and 24.