Denmark's Mark Pedersen took out the sprint from opening stage winner Marcin Bialoblocki, although there is no change in the general classification with Lang leading but on the same time to British riders James Moss and Richard Handley. Just six seconds separate the leading five riders.
Karwowski is third in the under-23 battle and 14th overall, 28 seconds from the yellow jersey with the remaining BikeNZ-PBR trio showing good strength to finish in the peloton and jump up the placings on general classification.
Meanwhile, Auckland's Dion Smith, injured in a crash on yesterday's tough stage, has successfully undergone an operation after breaking his wrist and radius.
Tomorrow's fifth stage is a 149km to the far north town of Buncrana on the Inishowen peninsula with five climbs including a category one test 13km from the finish.
Results, stage 4, 135km Westport to Burdoran: Mark Pedersen (DEN, Blue Water Racing) 2:55.36, 1; Marcin Bialoblocki (POL, Britain Giordana) same time, 2; Remi Sarreboubee (FRA, Aix en provence) at 2 sec, 3. Also New Zealanders: Cameron Karwowski at 9sec, 17; Piet Bulling at 15s, 17; Taylor Gunman same time, 33; Scott Creighton at 1:58, 73.
General classification after 4 stages: Pirmin Lang (SUI, Jakaroo) 12:47.45, 1; Richard Handley (GBR, Rapha Condor) st, 2; James Moss (GBR, Britain Giordana) same time, 3; Also: Karwowski at 28s, 14, Creighton at 2:24, 41; Bulling at 3:51, 52; Gunman st, 54.
Under-23 overall: Handley 12:47.45, 1; M Pedersen (BWC) at 19sec, 2 Karwowski at 28s, 3.