Several homes in Sydney’s west have been inundated with raw sewage after recent flash flooding caused septic tanks to overflow.

SES crews and emergency services were called to protect the swamped homes in Londonderry last night.

Six tonnes of sandbags were placed around the homes to stop floodwaters from swamping the properties.

Heavy rain in the area, described by one resident as “extremely bad”, has been blamed for the spillage.

Over 200mm of rain is expected to fall in Sydney over the weekend. (9NEWS)

“The water couldn’t go nowhere, it was all running down the street. Water down the gutters, in the shops, in the houses,” Londonderry resident Maria Galis told 9NEWS.

“It’s just unbelievable… The water couldn’t get away. There’s not enough drain pipes here.”

Resident Ms Galis reported floodwaters seeping through the glass windows and doors of her property.

She said that in her 50 years living in the area, she had only seen this kind of heavy rainfall once before.

Another resident, Mark Priestley, said his lounges and carpet had been destroyed during the flooding.

He added that the water rose so high, “It was like a swimming pool in my backyard”.

“I looked out the back and first thing I saw was my bin floating past my door,” Mr Priestley said.