The boats were found on Sunday evening on a section of the river running through Van Giang District in Hung Yen Province.
Boat ND-3593 extracted around 900 cubic metres of sand in the Thang Loi Commune area.
One of the boats seized for the illegal sand extraction
The crew locked the boat when detected by the police and tried to speed away. The boat's registration papers were invalid.
Boat ND-3861 was found with 200 cubic metres of sand. Two people on board should have shown paperwork related to the sand.
The police also seized boat HD-0482 as the four crew members failed to present legal papers related to the boat and sand extraction.
The four boats were impounded.
As many as 42 houses in Hanoi's Ba Vi District were recently damaged by severe erosion at a local embankment. The houses were located by the Da River and Red River banks adjacent to Phu Tho Province. Local residents blamed the problem on rampant sand-extraction activities on the rivers.
Following the case, Hanoi authorities have asked the Phu Tho People's Committee to suspend the licensing of sand extraction on the Da and Red rivers in the area next to Ba Vi District.