This is on the A5025 road, through the village of Benllech.
Diversions are in place.
Isle of Anglesey County Council said: “A5025 road through Benllech closed.
“A water main has burst on the A5025 road in the centre of Benllech.
“Road is closed so Dwr Cymru / Welsh Water can carry out repairs safely.
“The closure may be in place well into tomorrow.
“There is a diversion, along the B5108 to Brynteg and then along the B5110 Brynteg to Marianglas.”