A plane fighting bushfires near the national capital has dumped thousands of litres of fire retardant on one of Canberra's busiest roads.

Key points: A firefighting tanker hit turbulence and dumped 2,500 litres of fire retardant near the centre of Canberra

A firefighting tanker hit turbulence and dumped 2,500 litres of fire retardant near the centre of Canberra The pink chemical is not harmful to people, though questions have been raised about its environmental effects

The pink chemical is not harmful to people, though questions have been raised about its environmental effects The bushfire to the city's south has burnt out more than a third of the ACT

The air tanker was flying about 760 metres above the city when it hit turbulence at 3:30pm on Wednesday.

The jolt caused it to drop 2,500 litres of chemical retardant at the base of Anzac Parade, which leads to the Australian War Memorial.

The pink mess covered a large area, including Parkes Way, a nearby car park at Rond Terrace, and a large roundabout with a pond.

ACT Emergency Services Agency Commissioner Georgeina Whelan said no one was injured and the chemical spill posed no threat to people in the area.

"It's been a really challenging fire season," Ms Whelan told ABC Radio Canberra.

"We've run 495 sorties to date and dropped 3.6 million litres of retardant across the ACT and NSW from our aircraft.

"Obviously, we've seen a lot of pink all over the ground, we've had a couple of vehicles impacted — not dangerously, but they had the retardant spill on to them.

"And we had ACT Fire and Rescue on the scene almost immediately conducting the clean-up."

ACT firefighters cleaning up the spill on Wednesday afternoon. ( ABC News: Tamara Penniket )

The area was closed to vehicles briefly but did not significantly impede traffic.

The Emergency Services Agency advised the owners of vehicles covered with a light pink dust to wash it off with water.

Commissioner Whelan said that while the retardant posed no immediate risk to people's health, people who developed any irritation after coming into contact with it should visit a GP or a nurse-led walk-in centre.

The NSW Rural Fire Service (RFS) says the retardant used in firefighting operations is "essentially fertiliser (ammonium and diammonium sulphate and ammonium phosphate), with thickeners (guar gum) and corrosion inhibitors (for aircraft safety)".

"Current evidence does not suggest any significant effects on birds or mammals," a NSW RFS's information sheet says.

"However, in Australia, long-term fire retardants have been observed to cause effects on some species of native plants (leading to low-level damage to new growth).

"Water plants and animals are more sensitive to the effects of fire retardants … For this reason, pilots try not to apply fire suppressant retardants within 100m of waterways."