Premier Baird has asked employers to allow workers based in Sydney, Wollongong and Newcastle to leave early ahead of weather forecasts indicating conditions could deteriorate further on Tuesday evening.
"The storm ... between now and midnight could become more severe, particularly in the Hunter and the central coast," he told media.
"We're calling on ... bosses to be flexible, for people to make arrangements in an orderly way to start to head home as soon as you possibly can."
He asked those using public transport to be patient in the face of any storm-related delays.
The Sydney Morning Herald reported that The State Emergency Service had received about 4,500 calls for help by Tuesday afternoon, while triple-0 had answered 3,000.
Emergency Services Minister David Elliot labelled the weather event a "once in a decade storm" and urged people to use common sense while travelling.
"If you do not need to cross a road, don't do it. If you cannot see a road because of flooding, don't attempt to go over it," he said.
"We certainly need the people of NSW to take care when they're deciding whether or not to go home this afternoon and making sure they are going home in the daylight hours, if at all possible, because like any other operation, as soon as the sun sets and we're fighting with night time, this does make any rescue operation a little more difficult."
NSW Premier Mike Baird has urged bosses “to be flexible” in the wake of severe storm conditions. The storm front stretches from the Illawarra through to the Hunter and passes through heavily populated areas of Sydney.