Brisbane residents were told to take shelter in the strongest part of the house while “fast-moving and unpredictable” flooding in Currumbin Valley on the Gold Coast left residents cut off and unable to leave.

Forecasters expect Alfred to hit the Moreton Bay islands on Saturday morning before crossing the mainland coast later in the day, bringing damaging wind gusts up to 120km/h and dumping 350 to 450 millimetres of rain in a day in the worst-hit areas.

Destructive 155km/h wind gusts were no longer expected, the Bureau of Meteorology said just after 11pm on Friday (12am Saturday AEDT).

Millions from the Moreton Bay region north of Brisbane down into northern NSW were under emergency warnings to take shelter on Friday night.

“Go to the strongest, safest part of the building you are in. This will be away from big windows,” authorities advised Brisbane residents.

“It could be a bathroom, walk-in wardrobe, or hallway. Stay there.”

In Currumbin Valley, residents were told it was too late to leave to avoid “dangerous, widespread, fast-moving and unpredictable flooding occurring near Currumbin Creek”.

Authorities said evacuation routes were closed and homes and buildings would be flooded.

The rare cyclone’s fury was already apparent long before making landfall as it ripped up trees across the Gold Coast, knocking out power to 130,000 homes and businesses in south-east Queensland and almost 40,000 more in northern NSW before midnight.

At 8pm on Friday (9pm AEDT) Energex said it had managed to restore power to thousands of properties throughout the day but would only be responding to emergency situations where it was safe.

“While our crews have been fixing faults today where it’s been safe to do so, cyclonic conditions aren’t safe work environments,” the power company said.

“Our teams are awesome but they’re not bulletproof: we’re not putting them at risk.

“Also, practicality: In most cases, it doesn’t make sense to begin network repairs when there will likely be more damage to come.”

Potential tragedy struck on Thursday afternoon inland from Coffs Harbour when a man’s four-wheel drive was swept from a Wild Cattle Creek Bridge at Megan.

Police said he was able to escape and speak with them as he clung to a tree branch about 30 metres from the bank but was swept away beneath the water just after 3pm.

Police and SES searched the area but found no sign of him, sparking a reminder to stay away from flooded roadways.

The incident followed five flood rescues overnight into Friday.

“There is always going to be rare situations when people can get trapped or isolated, and we need to reach out to them and rescue them in that context,” SES NSW Commissioner Mike Wassing said on Friday morning.

“These rescues are about people driving into floodwaters.”

Authorities were also begging Gold Coasters to stay away from the closed and dangerous beaches, threatening $16,000 fines.

Wind gusts faster than 100km/h were recorded on the Gold Coast throughout the day as trees were ripped up.

One fell on a woman’s home in Mudgeeraba about 4.30am (5.30am AEDT), waking her when it crashed through her roof.

“She was holding up the ceiling in her bed so it wouldn’t cave in on her,” neighbour Alex Nash told 9News.

In Coolangatta, a large Norfolk Island pine tree, which has stood in its spot for more than 30 years, was uprooted.

But it’s feared flooding will be the major concern as Alfred devolves into a tropical low and dumps relentless rain after making rainfall.

Basically all of the regions’ major rivers are expected to be affected and more than 15,000 people have been ordered to evacuate across northern NSW, particularly in Lismore.