On a day of total fire ban in Sydney, dozens of blazes kept firefighters busy across the state.

Authorities warn they'll throw the book at arsonists, with an emergency strike force to hunt down those who light fires.

At Teralba, in Lake Macquarie fire crews were battling a blaze in scrub this afternoon. Thick smoke covered the rail line as crews worked to keep nearby homes safe.

Outside of Dubbo a grassfire destroyed a barn. The fire's progress was being closely tracked by emergency officers in Sydney.

Investigators also hunted suspected arsonists responsible for a fire which swept through parts of St Mary’s last night.

Fears of a bad fire season ahead have seen police re-activate strike force Tronto, which focuses on firebugs.

They risk 25 years jail for endangering life with bushfire, 14 years for recklessly starting a fire. One year and heavy fines for ignoring total fire bans.

Of those investigated around 100 bushfires each year are found to be deliberate lit. Better organised and more sophisticated fire authorities mean arsonist are at more risk of being caught.