A single-vehicle crash has caused chaos – and hundreds of litres of human portaloo waste – to foul up a main South Island road.

Emergency services were called to the crash on SH1 near Arundel Belfield Rd, near Geraldine, just before 2pm to reports that a truck carrying portaloos had crashed and was leaking human waste.

While it was initially reported that 3000 litres of human waste had dispersed, Fire and Emergency Shift Manager Ryan Dawson said further evaluations confirmed it was closer to 500 litres.

Dawson said a priority for crews was containing the waste and ensuring it doesn’t spread further.

Crews are treating it as a hazmat incident.

The road has been reduced to one lane while emergency services are at the scene.

No injuries were reported in the crash.