Canterbury/Westland decreased to 42.2, its lowest level since March 2011, while the Otago/Southland region took a significant hit, declining to 38.3 points, its lowest level of activity since March 2009.
Among the sub-groups, food, beverage and tobacco was one of the few stand-outs on 54.0 points, even as it slipped from 63.1 in March.
Petroleum, coal, chemical and associated products fell to 40.6 points, machinery and equipment manufacturing dropped to 41.7, while metal manufacturing dropped to 47.7 points.
Steel said the drop could be attributed to several things, including ongoing uncertainty in Europe, a slowdown in Australia and the strong New Zealand dollar.
"The April PMI dip can be sheeted back to the New Zealand dollar, either through its general persistent strength or the important New Zealand dollar/Australian dollar crossrate for manufactures hitting a seven month high in April," he said.
"We will be on the lookout to see if the dip in April's PMI is a precursor to a softening in other business survey's across a wider range of sectors."
The drop in activity also led the proportion of negative comments increasing to about 58 percent from 52 percent.
Globally, the JPMorgan Global Manufacturing PMI stood at 51.4 in March, helping to signal a modest expansion in world manufacturing for the fifth month in a row.