Traffic on SH3 south of Mokau will be down to one lane until long-term protection measures can be re-installed on the cliff face, the NZ Transport Agency says.

A major slip came down on the road on Sunday following a large amount of rain over the weekend.

"Our geotechnical engineers have advised us that there is still a risk to road users if the southbound lane is re-opened," NZTA regional performance manager Karen Boyt said.

"We expect that it will take around two months to re-install the protective mesh that will help prevent further slips onto the road. Until the installation is complete we will continue to operate this section of the road as one lane under stop/go control, and motorists may experience minor delays.

"We will have contractors on site 24/7 to ensure that traffic flows smoothly and to provide on-going monitoring of the rock face so that they can spot any risks of further rock fall.

"In the short term we will continue to use an abseil team to help shift loose rocks safely, and then contractors will start the installation of the protective mesh, so motorists will notice crews working on and around the cliff face. We remind motorists to keep their eyes on the road as they travel through the slip site.

"We appreciate motorists' patience while our contractors work hard to get this important route between Taranaki and the Waikato re-opened. Two hundred cubic metres of rocks and dirt - enough to fill three, 40-foot shipping containers - were removed.

"While we can't completely remove the risk of a major slip happening again on this site, the protective measures that we will put in place over the next couple of months will go a long way to help protect road users from any further major slips."