By yesterday evening more than 71mm of rain had lashed Bellambi and almost 50mm fell at Albion Park, causing flash floods and leaving roads impassable.

Emergency crews were called to Osborne Parade, Warilla, about 3.40pm after lightning hit a two-storey home and blasted a large hole in the roof.

Five minutes later a house was struck at Berkeley Rd, Gwynneville, causing a power surge.

Leaking roofs, downed trees and flooding kept SES crews busy as they answered 38 calls for help between Thirroul and Koonawarra.

Among them was Bulli Hospital, where a storeroom and medical records were flooded.

Heavy rainfall caused delays on the South Coast rail line after track problems at Austinmer led to major delays of peak hour services late into the evening.

Police were called to several minor accidents as drivers failed to slow down in the deluge.

Chief Inspector Mark Lavers urged people to take care during the wet weekend ahead.

"Drivers are going too fast, they have to slow down," he said.

"We're expecting more rain so I hope people will be sensible, drive to the conditions and don't drive if you don't have to."

The downpour forced several major road closures, including at Macquarie Pass where overnight rains caused a landslide and extensive damage to the roadway.

It was reopened about midday.

A rockslide left rocks and debris littered across the road on the Princes Hwy at Bulli Pass about 5pm, forcing the closure of the northbound lane.

Blacked out traffic lights at Kemblawarra and Corrimal caused peak hour traffic congestion, and a flash flood in the Westfield Figtree carpark about 3.30pm left 10 cars submerged in water.

A fallen tree on Mt Keira Rd at 6pm blocked both lanes for an hour.

The Bureau of Meteorology has issued a severe thunderstorm warning for the Illawarra this weekend, with heavy rain and thunderstorms forecast and flash flooding expected.