The blast followed a dispute over the sandbag flood barrier at the lower line of Khlong Hok Wa in the district.

Police found debris of what appeared to be a brick attached to gunpowder. The package was thrown onto the bridge across the canal where around 100 residents were trying to close a 70m-wide gap in the barrier.

Police said the incident was aimed at stirring up a confrontation between residents on both sides of the flood barrier.

Crowd-control police from the Metropolitan Police Division 2 were deployed to beef up security.

Ratchapol Boonrod, deputy district chief of Sai Mai, said residents from tambon Lat Sawai of Pathum Thani's Lam Luk Ka district removed sandbags from the flood barrier.