An explosive device was hurled toward a crowd at a riverside pier in the heart of the Thai capital but apparently missed its target on Tuesday, police said.
The bomb was apparently tossed down from a foot bridge above the pier on the bank of Chao Praya River in Sathorn area and dropped into the water, causing a loud, harmless blast.
Nobody, including those who were waiting for passenger boats on the pier, was killed or injured, the police said.
Just above the pier is a usually-crowded, elevated railway and Taksin Bridge over the Bangkok river.
The mysterious bomber who immediately fled the scene could not be identified as yet and is still at large, the police said.
Explosive Ordnance Disposal units dived into the water in search of evidence pertaining to the attempted bombing.
That followed Monday's blast at Rajprasong intersection which killed over 20 people, including tourists, and injured more than 100 others.
Among the slain victims, most of whom were Thais, five were from China, two from Malaysia and one from Singapore.
The TNT bomb was laid near a shrine at one corner of the busy intersection visited by Thai and foreignworshippers.
Premier Prayut Chan-o-cha condemned the inhumane bombing and called on members of the public to cooperate with the authorities.
He vowed to bring the bomber, suspected to be an unknown foreigner, to justice and called on the public to stay calm and watch out for any hint and sign of any untoward incident throughout the capital.
Other areas where people were given alert warning and suggested to exercise utmost caution following the Rajprasong blast included Khaosarn Road, Silom Road, Sukhumvit Road, Thonglaw Road, Narathivat Road, Victory Monument area and Patumwan intersection.