People are being kept in temporary jail facilities with no natural light and with limited shower access for up to four days while others are kept in even more rudimentary police cells without seeing a magistrate because of the state's overcrowded prisons, the NSW Law Society says.

As new figures reveal an explosion in the remand population since the state government introduced tough new bail laws last year, the NSW Law Society's criminal law committee has written to the head of Corrective Services, expressing serious concerns about the flow-on effects for those who have just been taken into custody.

Overcrowded jails are stretching temporary cell facilities beyond their limits.

The committee, made up of private criminal lawyers and representatives from Legal Aid NSW, says people are being held for days in correctional centres which are designed to temporarily hold accused persons before they go to remand because the state's remand centres are full.

The temporary facilities have, in turn, become full at times, meaning that people taken into custody have spent long periods in suburban police cells which are even more basic.