Drone shot of Manawatu Gorge slip, blocking State Highway 3 at the Woodville end.

The Manawatu Gorge road is closed after slips blocked both lanes, with the cleanup expected to take weeks.

The NZ Transport Agency first said both lanes were blocked after one slip on State Highway 3 at 9.30pm on Monday.

The NZTA then posted on its Twitter and Facebook accounts on Tuesday afternoon that there were multiple slips and that the road would be closed until May 25.

SUPPLIED/NZTA This smaller slip at the Ashhurst end of State Highway 3 through the Manawatu Gorge is expected to take a day to clear.

However, those posts were soon deleted and replaced with ones only saying there were multiple slips.

Highway manager Ross I'Anson​ said there were two slips, with one much bigger than the other.

SUPPLIED/NZTA About 3,500 cubic metres of earth is blocking the Woodville end of State Highway 3 through the Manawatu Gorge.

The small slip, at the Ashhurst end of the gorge, was about 200 cubic metres and would take about a day to clear, he said.

But the bigger slip, at the Woodville end, was about 3500cum.

While both slips were small in comparison to a 2011 slip that closed the road for a year, it would still take three weeks to make the road safe again, I'Anson said.

Murray Wilson This slip, in 2011, closed the Manawatu Gorge for a year.

Geotechnical engineers and NZTA staff had done a preliminary assessment of the slips with a drone to make sure it was safe for work to start on clearing and stabilising, he said.

More detailed analysis work would take place at 9am on Wednesday before deciding on the next steps.

Motorists can use the Pahiatua Track and the Saddle Rd as alternative routes.

The highway through the gorge has a history of being closed because of slips, the most famous being two in 2011.

The road was closed from August 2011 until August 2012, at first opening to just one lane.

Slips continued to plague the road, which only fully reopened to two-way traffic in November 2012.

Clearing all the slips cost NZTA more than $20 million, while businesses in the area were also hit hard.

A $2.2m gorge upgrade programme began in September 2015, including the installation and repair of rockfall netting and other protective measures in the gorge.

The latest work, which started in February and was due to be completed in April, focused on clearing debris from the 2011 and 2012 slips to stop it reaching the road.

The main alternative routes, the Pahiatua Track and Saddle Rd, have also had their fair share of issues.

The track, a main route between Manawatu and Wairarapa, was fully blocked for a few days in early April after Cyclone Debbie.

Meanwhile, the Saddle Rd has in the past been damaged by heavy trucks and increased traffic when the gorge is closed.

About $8m has been spent upgrading the road in the past few years.