Big blaze at SA mulching business

A large fire at a soil and mulching business north of Adelaide is still burning, with the damage bill already estimated to be $6 million.

The fire at the Jeffries plant at Buckland Park began about 4am on Monday.

A Country Fire Service spokesman says 100 emergency personnel and 20 appliances are at the fire, which is likely to continue burning throughout the day.

Smoke has reduced visibility in the area and residents who suffer from respiratory or cardiac conditions have been advised to close all windows and doors and stay inside.

"The estimated damage bill is about $6 million but a further assessment will be carried out when the fire is under control," the CFS spokesman said.