The CFA's operation officer for Casey, Cliff O'Connor, said the deluge caused some internal "false" suspended ceilings in the centre to collapse, although there was no structural damage to actual ceilings.

There was a small fire in one of the main electrical switchboards that was quickly extinguished and some alarms went off after water affected the electrical systems, Mr Connor told the Journal last Friday.

"Water obviously backed up through the stormwater system, cascaded through the roof and found its way back into the plasterboard and the suspended ceilings."

He estimated water on the Princes Highway and Magid Drive near the centre reached the top of car tyres.

A Westfield spokeswoman said clean-up crews worked through the night to ensure most of the centre could open on Friday. Twelve outlets, including the cinema complex, stayed closed.

The shopping centre did not reopen until it received the all-clear from safety inspectors, she said.

Meanwhile, the Narre Warren SES unit received 117 requests for assistance, with the Berwick area accounting for 77 of these calls.

The worst-affected street in Berwick was Marisa Crescent, where a fallen tree caused a traffic hazard.

Most calls for help related to trees or minor flooding from overflowing gutters.