Police numbers need to be increased to keep up with population growth, the founder of an Auckland crime prevention group says.

Stop Crime New Zealand is holding a march in Manukau today to express growing frustration at a spate of brutal dairy and liquor store robberies in Auckland.

Group founder Sunny Kaushal says every week he deals with new cases of shopkeepers and taxi drivers being brutally robbed and attacked, and has heard of at least 30 robberies in the city in the last month, mostly targeting shopkeepers and taxi drivers.

He says most offenders get away with their crimes because police aren't tough enough and there aren't enough police to investigate and enforce the law.

Kaushal says only yesterday afternoon he spokes with a Chinese family who were robbed in broad daylight in busy shopping area in Mt Wellington.