The city's transport network has held up well in the face of the storm despite flooded train stations and traffic jams delaying commuters across the city, the state government says.

"It was much better than it otherwise would have been," Premier Mike Baird said on Wednesday of the effectiveness of commuters' response to a state government appeal to stagger trips into the city.

About 15,000 homes were still without power across Sydney on Wednesday morning - a figure that rose to 130,000 homes in the Newcastle and Hunter region, as well as 80,000 outages on the Central Coast.

Mr Baird signalled that the areas to be covered by a natural disaster declaration would be finalised within the next 24 hours as conditions eased, but reiterated a plea to avoid non-essential travel for Wednesday.

"The advice is there will be an easing both in terms of the rain and winds and that is good - but at the same time, the expectation is the winds will continue and there will be flash flooding - so, particularly [in] areas that have already been severely impacted by this, there is a real concern," Mr Baird said.

"The weather still remains dangerous and the conditions are dangerous so this is not a time for complacency."

State Emergency Service commissioner Adam Dent urged people to stay away from floodwaters, noting that about 100 people "either by accident or by act", had needed to be rescued since the weather event began.

"If it is flooded, forget it. You're putting your own life and the lives of our members at risk."

Commuters faced lengthy delays on Wednesday morning, particularly in Sydney's west and inner west.

Services are delayed or changed on about half of Sydney's eight heavy rail lines this morning.

The Airport, Hunter, Central Coast and South Coast lines remain fully or partially closed. The Transport Management Centre said buses were being sent to replace services.

The Bankstown line was partially closed between Campsie and Sydenham about 11 am, because of a fallen tree. Commuters have reported being stuck at stations around Campsie.

There have also been lengthy delays on the Inner West and South Line this morning, but the line has been re-opened after an early morning closure caused by flooding at Lewisham and Marrickville Stations.

Tracks at Marrickville station were completely submerged about 7am.

The tracks were pumped clear and services resumed an hour later but trains were delayed by up to 30 minutes and travelled at extremely slow speeds. Flooding at Lewisham station has also cleared but remains deserted.

There are also widespread reports of hazards and lane closures affecting Sydney motorists across the road network, particularly north- and south-bound traffic from the city centre and routes to the western suburbs.

Traffic on the M4 in Sydney's western suburbs has reached a standstill, motorists say.

A northbound land is closed around Wentworthville and a western lane is closed at Auburn, while motorists say emergency workers are working to clear flooded exit ramps around Silverwater.

Transport Minister Andrew Constance warned it would take "a couple of days" before services in the CBD were restored to normal. "Please be patient".

Mr Baird reiterated appealed to city workers and their employers to again vary the time at which they travelled home.

"If you have the capacity to be flexible in coming to or leaving work, then do that," Mr Baird said.