The American mother and daughter lost in the Tararua Forest Park possibly made a mistake while hiking a popular day loop track and ended up off the track.

A search and rescue operation yesterday resumed at 5.30 this morning after Carolyn and Rachel Lloyd's car was found at the entrance of the Kapakapanui Track in the park near Waikanae yesterday.

Sergeant Anthony Harmer said the track the mother and daughter are believed to be on is steep and can be deceptively difficult in places.

"There are a couple of places where people can make mistakes and end up off the track and we are looking at that possibility this morning."

Two dog teams, helicopters and 4WD are being used in the search this morning and police are appealing to anyone who may have seen two women on the track in the past week, or anyone who may have seen their vehicle, a silver Toyota Yaris hire car, registration DLZ 347.

Four teams of eight people were searching for the missing pair, with a mix of police and search and rescue volunteers.

The back window of the the rental car had been smashed, with glass visible inside the car.

Police were unsure if the glass was broken before or after the two went missing.

There is no cellphone coverage on the remote Kapakapanui Track.

One marked and one unmarked police car are at the scene.

A group of media has also gathered at the entrance to the track.

Trampers are being questioned by police as they enter and exit the track.

Miss Lloyd, a 22-year-old Massey University student, and Mrs Lloyd, a 45-year-old who was visiting her daughter from the United States, were due to check out of their Palmerston North Motel on April 27. They were also expected to return their rental vehicle at 11am yesterday.

Family members, the rental company and the motel have not heard from either of the women.

Police confirmed that several people had seen the missing pair on the track at the beginning of the week, Radio NZ reported.

The track is steep, rough and muddy in places and it's classed as an advanced walk.

It is a six-to-eight-hour loop track.

"The climb is steep and the track rough and muddy in places," DoC's website reads.

Carolyn is visiting from the United States. Her daughter Rachel is a student at Massey University.

Rachel has worked as a research assistant at North Carolina State University, where she was studying political science. She was the valedictorian of the December graduating class and won the Outstanding Graduate Award.

She also volunteered for an organisation which aimed to help prevent blindness.