The eight-hour voting started at 8am on Saturday.
Returning Officer Mujibur Rahman said they had marked 105 polling centres out of 140 as sensitive.
Four candidates are in the fray.
They are Awami League’s Abdul Wahhab with ‘boat’ symbol, Kazi Touhidul Alam of NPP with the ‘mango’ symbol, BNF’s Mutasin Billa Rifat with ‘television’ symbol, and independent candidate former Awami League leader Tapan Kumar Roy with ‘lion’ symbol.
Returning Officer Rahman said 50 mobile teams of police, RAB, BGB and Ansar, nine special mobile teams and eight strike force teams with 4,000 personnel in all had been deployed.
Six mobile courts headed by judicial and executive magistrates were also deployed.
The constituency fell vacant after Awami League MP Muhammad Serajul Akbar, who was MP for four consecutive terms, died on Mar 9.