About 20 grenades were reportedly used in the area, according to latest reports.
The first grenade came shortly after midnight near Gate 4 of Lumpini Park near the Thai-Belgian flyover.
Gunshots followed in the area, as well as near Sala Daeng and Surawong Roads and Henri Dunant intersection.
From 1.55am to 4am, more than 18 blasts were heard near Henri Dunant and Sarasin intersections while gunshots were reported around Thai-Belgian flyover. However, the attackers could not enter the area around the stage.
Vendors on Thaniya and Silom roads said they heard the blasts for almost two hours from before 2am. None of them were injured.
At 3am, PDRC guards extended their road closure to Thaniya intersection and searched the area for suspects. Reporters and police were not allowed to enter.
There were reports that the People's Democratic Reform Committee (PDRC) guards caught a suspect, a taxi driver who tried to flee to Rama IV Road heading for Hua Lumphong train station.
Suchart Srisung posted on his Facebook page at 4pm that very loud explosions were heard near Gate 5 of Lumpini Park at 4.11am, forcing a shutdown of the park.
A Lumpini station police officer confirmed three guards were shot at Gate 4.