King tides are bringing new dangers to a huge stretch of Australia’s east coast that has already been battered by days of heavy rain and damaging winds.

Authorities warn that a 500-kilometre front that hit the coastline from Bundaberg to the NSW border at the weekend will still pack a punch for several more days.

Queensland Emergency Services Minister Mark Ryan said residents must prepare for the worst.

“Many of the impacts from this weather event will be similar to a category-one cyclone event,” he said.

Record high tides were due in the area about 11am (AEDT), exacerbating fears of damage to areas such as Byron Bay’s main beach, which has already been hit hard by erosion.

A walkway has collapsed into the ocean and there are concerns for beachfront properties.

Pictures show the sand on Main Beach was inundated with water overnight. By Monday morning, it was clogged with fallen trees.

Tweet from @BOM_Qld

The BOM has issued a flood warning for the Bellinger River at Thora and Bellingen. It will affect the towns of Byron Bay, Tweed Heads, Lismore, Grafton, Coffs Harbour, Bellingen, Nambucca Heads and Kempsey.

The weather bureau has also warned of more rain and storms next week, with those conditions continuing until Christmas.

The low-pressure system off the south-east Queensland coast on Monday was expected to bring another round of heavy rain and strong and damaging winds, with gusts of more than 100 km/h in some area.

The Tweed River at Tumbulgum is likely to reach the minor flood level (1.4 metres) with Monday’s high tide while the Bellingen River is expected to reach minor flood level (3.7 metres) at the Bellingen Bridge.

The SES warned farmland downstream of Bellingen might begin to be inundated.

There have also been waves of up to 10 metres on the Gold Coast, with Surf Life Saving clubs and coastal resorts on high alert as people still risked swimming and surfing in dangerous conditions.

“An anxious time for staff at Rick Shores on the Gold Coast. Water is coming far too close for comfort. Staff are doing all they can but conditions are expected to worsen,” wrote Network Ten journalist Jacob Chicco, posting footage of the king tide engulfing a beach carpark at Currumbin.

Tweet from @JacobChicco

Further north, there was surface flooding on beachside roads on the Sunshine Coast, while waves had breached the northern end of Bribie Island by mid-morning on Monday.

The NSW State Emergency Service had more than 700 calls for help over the weekend, and carried out at least five flood rescues as a cyclone-like deluge hit the state’s north.

There were a similar number of callouts in Queensland, where the weather bureau was forecasting even worse conditions on Monday, with the possibility of flash flooding from mid-north Queensland down to the NSW coast.

Up to 150 millimetres of rain is expected in the already drenched area from mid-morning on Monday.

Queensland Fire and Emergency Assistant Commissioner Kevin Walsh said Monday’s conditions would be challenging.

“All of the catchments are now fully saturated so any rain that we get later today can cause us some harm,” he said.

Tweet from @RACQOfficial

In NSW, SES spokesperson Ilana Pender-Rose said more heavy rain was expected throughout the day in parts of the mid-north coast and northern rivers regions.

“Flash and riverine flooding are the biggest risks up north with this system,” she told the ABC.

Tweet from @rodcu

In Byron Bay, the famous beach has all but disappeared, as the king tides bring severe coastal erosion. The beach has been completely covered with water, with fallen trees along the coast also causing issues.

Sandbags are helping to protect the most vulnerable businesses. Beach Restaurant owner Ben Kirkwood said recently installed flood defences were doing their job.

“I would say if it wasn’t for the wall we wouldn’t be here right now. It’s doing its job. Thank goodness it got installed when it did,” he told Nine’s Today on Monday.

“Down the other area of the beach, the Main Beach, it’s taking a hammering.”

Tweet from @bengrubb

BOM senior meteorologist Dean Narramore said there had been  “massive” beach erosion along the coast up to south-east Queensland.

“This morning we’ve observed waves offshore around the eight metre mark,” he said.

“We’ll see a big king tide today, very high tides again tomorrow.

“We could see waves of three-to-five metres come into shore … today and into tomorrow.”

On Sunday night, the SES contacted hundreds of residents in the Tweed and Byron Bay areas to warn them of heavy rain and dangerous flash flooding.

The Tweed and Brunswick River Valley had rapid creek rises early on Sunday, with 415 millimetres recorded just across the Queensland border.

The Bureau of Meteorology has warned that the sustained heavy rain, damaging winds and flooding, as well as dangerous surf conditions, in the area are likely to last all week.

It is also warning about more showers and storms next week, with those conditions continuing right until Christmas.

-with agencies