Police were alerted at 6pm when the three 22-year-old women and girl failed to return, and the car in which they had been travelling was later found by police parked in Silverstream Valley Rd, less than a kilometre from the Waiora Scout Camp.
Friends or family members said they had not been in contact with the group since 4pm, and, after apparently making some initial checks in the area themselves, they contacted police.
A police spokeswoman said conditions were mild last night, but police were keen to contact the missing people as soon as possible because they had not expected to be in the area overnight, and because of the child.
It was unclear what they were wearing, but the missing people may have been dressed relatively lightly. Volunteers from the Land Search and Rescue group were among the 35 searching last night, in a "full search and rescue operation", but details about the number of searchers were not immediately available, the spokeswoman said.
Police last night also appealed to the public for help in their search, and asked any property owners in the area to contact police if they had seen the missing people.