Streets in the South Island tourist towns of Wanaka and Queenstown were slowly going under water on Friday, after Lake Wanaka and Lake Wakatipu burst their banks earlier in the week, flooding businesses and sewerage systems.

Water and large debris closed the main street of Wanaka, a popular spot with Instagrammers thanks to its famous tree that appears to have grown out of the lake. On Friday businesses were sandbagging as heavy rain continued to fall.

Sewerage systems in the town were also at risk of contaminating the lake, with the Queenstown Lakes District council taking the precautionary measure of shutting down the sewer connection to a handful of premises.

Wanaka residents were told to be on “high alert” with heavy rain predicted all weekend.

The streets of the usually bustling tourist town were largely empty, and the popular cafes and restaurants on the lake shore were closed.

The extreme weather event has seen more than a month’s worth of rain fall in the space of a week. The Met service said a weather system moving up from Tasmania was mostly to blame and it was possible the Australian bushfires had also contributed, with dust particles causing more cloud and rain systems to form in the west of New Zealand.

Met Service meteorologist Stephen Glassey said the average rainfall in Wanaka for December was 54mm, and this week 81mm has already fallen. More than half a metre of rain had also fallen in some areas of the Southern Alps, flowing down the river catchments and causing the lakes to swell further.

“It’s possible that some of the particles from the Australian smoke and dust can act as cloud condensation nuclei which can enhance the rainfall, but I don’t know if we can prove that conclusively,” Glassey said, of what has caused this extreme weather event.

“It is definitely worth further investigation.”

Michael Donald, owner of Lakeland Wanaka on the foreshore, has spent days wading through the flood waters in an attempt to protect his business.

“A lot of the rain has been caused by the dust particles from Australia, and with the late spring storms, it’s been a really bad combination,” said Donald.

Sandbags and black plastic sheet line the front of many lakefront businesses in Wanaka, as residents prepare for rising flood water. The lake levels are expected to peak tomorrow, but the bridge at Dinosaur Park is already fully submerged. @rnz_news @CheckpointRNZ pic.twitter.com/GIvQe4NitT — Tess Brunton (@TessBrunton489) December 5, 2019

“There’s more rain coming this afternoon, obviously the worry is that is takes 24 hours for any rain that’s fallen on the hills to make its way down to the lake, so even if it stops raining we’ve still got 24 hours of the Lake continuing to fill up.”

In nearby Queenstown, more than 200 high school students were evacuated by helicopters and four-wheel drive vehicles after their remote school camp on the edge of Lake Wakatipu began flooding.

Shops in the tourist resort had also started sandbagging, but the threat of inundation was less severe than in Wanaka, where businesses are located closer to the lake’s edge.