Searchers looking for two trampers missing in the upper South Island are pulling out of exposed areas because of heavy rain

Concerns are deepening for Jessica O'Connor and Dion Reynolds as 100 millilitres is expect to fall in the area in the next 24 hours.

An aerial shoreline search from the Kahurangi Lighthouse north to Farewell Spit failed to locate the 23-year-olds.

A police spokesperson says search efforts will focus on lower areas during the heavy rain, and teams in more exposed areas will pull out for their safety.

The trampers set out from Anatori on May 9 and were due back on May 14-15.