Snow on the Lewis Pass means the alternative highway between Picton and Christchurch will remain closed overnight for safety reasons.
The Transport Agency said trees were buckling under the weight of the snow, and it was also making the edges of the highway dangerous.
Road crews will be working through the night, but it was unlikely that the Pass would reopened until daylight tomorrow.
The road was reopened for a short time this morning after contractors cleared snow that had caused four trucks to jack-knife.
NZTA spokesperson Tresca Forrester said the decision to close a major highway was not made lightly, but to protect road users.
She said drivers now needed to stop at the highway checkpoints for their own safety.
A worker at the Springs Junction garage said it was gearing up to feed the line of stranded truck drivers.
Stephen Baker said a line of more than 25 trucks was now extended down the road outside the garage, with drivers now getting ready to spend the night in their vehicles.
"A lot of them have got their own sleeping arrangements in their cabs, so they'll sleep in there, and we'll feed them. With these trucks these days, they're hooked up to electric blankets and all that type of stuff."