Too many day walkers are being booked on the Milford Track without permission, the Department of Conservation says.

All eight companies offering the guided day walks were this month discovered to be overbooking and in breach of the limits imposed under their concessions or permits, department spokesman Martin Rodd said.

Breaches by two of the companies were so bad the department last week suspended them from operating, though the suspensions were later withdrawn for fear of disappointing hundreds of mainly Japanese tourists.

Companies were supposed to take no more than 12 people and a guide on any one trip. But in the worst cases, the department found some of the day trippers were in packs of up to 36 people. The large numbers were putting pressure on the huts and the toilets on the track.