Police said the grenades were fired into the crowded fair selling products native to the area opposite Bacho district police station at about 7.20pm.
Four security volunteers and 12 fair-goers sustained shrapnel wounds.
Some of them were also trampled by panicked people trying to flee the scene.
The injured, who were not identified, were taken to Bacho Hospital.
Authorities closed off the fair venue as forensic experts were due to arrive at the scene this morning.
Meanwhile, five people died in separtate attacks in the far South yesterday.
In Pattani, Sen Sgt Maj Mustorfa Laehae, 44, of Pattani police station, was killed in a drive-by shooting in Ban Sue Dung in Sai Buri district. He was shot in the head and died later in hospital.
In Yala's Muang district, a woman was killed and her husband seriously injured in a drive-by shooting. The victims were identified as Saowaluck Sitthiphan, 29, of Ban Na Tham in Muang district, and her husband Prinya Sitthiphan, 31, a technician at the Yala irrigation office.
They were travelling on a motorcycle around 8am in Ban Kampan in tambon Tha Sab when a gunman riding pillion on another motorcycle fired at them with a handgun.
Also in Yala, a woman was seriously wounded in a drive-by shooting on the Yala-Batong road at Ban Ka Sode in Bannang Sata district. Duangnate Kamsri, 34, of tambon Tham Thalu in Bannang Sata, was shot in the torso.
In Yaha district, Kuem Sukkarn, 72, a resident of tambon Tachi, was shot dead as he rode his motorcycle to a market.
In Pattani's Muang district, a traditional medicine trader was shot and killed outside the central mosque.
Mama Arwae, 43, was selling medicine at his stall when two men on a motorcycle fired shots at him. Police said Mama worked as a police informant.
In Narathiwat, a woman was killed and her husband severely wounded in a gun attack on their pickup truck in Rueso district. Sunthorn Nakthong, 50, was driving his wife Jittima through Ban Tango Patae when gunmen fired at their vehicle.