More than 1,000 volunteer firefighters were called into action as the wild fires fanned by hot winds of up to 100 kph broke out in more than 50 locations across the state, killing one man and destroying at least seven homes across the state.
Investigations are continuing into the cause of many of the fires, but Mr Koperberg said a number of them are thought to have been the work of arsonists.
"Without wanting to pre-empt the investigations, you will find the majority were due to either fallen powerlines or mishap of one description or another," he told Macquarie Radio.
"But a significant number would nevertheless have been deliberately lit."
The bushfires and winds yesterday caused power blackouts to more than 100,000 homes in the southern highlands, western Sydney and the south coast and burned out more than 2,000 hectares of bushland.
Emergency crews are still working to restore electricity to areas in Sydney's north and west, the Blue Mountains and the Central Coast.
Worst ever season
Extreme conditions, the hottest, driest August on record and much of the country in drought, means Australia is facing the worst fire season ever, according to bushfire expert Kevin O'Loughlin.
Mr O'Loughlin, from the Bushfire Co-operative Research Centre, says the massive fires in New South Wales, combined with bad fires in Victoria last week and the 200 fires already reported in Tasmania this month - could be a taste of things to come.
"Just looking at what we've seen already, this is a major concern," he told ABC Radio.
"We've got to get a greater understanding on this, on the frequency of fires, the earlier start to the season and if there's any connection to climate change."
Mr O'Loughlin said the dangers were heightened by the increasing number of people living in areas at risk of bushfire.
More Victorian firefighters
Meanwhile, Victorian Environment Minister John Thwaites said 200 seasonal firefighters are being hired and will start work earlier than usual to help prepare for the fire season.
"We have been doing fuel reduction burning and seeking to do it earlier, but the conditions are so dry and so adverse that we're already having to wind down fuel reduction burning," Mr Thwaites told reporters.
He said firefighters are already in the in the process of building trails and fire breaks in key areas. "We are very concerned that this summer will be one of our worst bushfire risks ever.
"The state is extremely dry. We've had 10 years of below-average rainfall. Areas like the Otways and the Dandenongs, which weren't burnt in the 2003 fires, are particularly at risk,” Mr Thwaites said.