2 people remain in Garda custody in Ballina this morning following a series of raids by gardai yesterday in 4 separate growhouses across the state

Senior gardai say cannabis growhouses now pose one of the main challenges to law enforcement in Ireland.

It follows the seizure of more than six thousand cannabis plants in four separate locations yesterday

It brings the number of plants seized to record levels under a nationwide operation, codenamed Nitrogen and spearheaded by the garda national drugs unit.

The seizures yesterday were made in Swinford, Co Mayo where plants with a street value of (€1.4m) were seized, Tramore, (€1.6 m),  Ardee, Co Louth (€1.2m); and Newbridge, Co Kildare (€800,000).

The combined street value of the seizures worked out at €5m. All of the growhouses were located in industrial units in the towns.

Three Chinese men and two Poles were arrested and are all still in custody this morning at garda stations in Ballina, Tramore and Drogheda.