Marlborough Civil Defence is warning campers to move to higher ground and make sure tents are secure - heavy rain and strong winds are forecast to lash the region.
Up to 150 millimetres of rain and wind gusts of 130 kilometres an hour are expected for the region from midnight on Monday until midday on Tuesday.
A major downpour of up to 300 millimetres is also due for neighbouring ranges near Nelson.
A civil defence controller, Ross Hamilton, says campers need to heed the warnings. He urges people to camp well above high-water level, and not to try crossing swollen rivers.
Mr Hamilton says campers should also set up in a sheltered spot to protect themselves from the wind.