Council workers were left scrambling to close the bridge around 11am as the Bellinger River executed a "hockey stick" rise.
Normally there's a bit more warning, but sodden catchments and heavy rainfall this morning saw the river rise by two metres between 9am and 11am.
Lavenders Bridge divides the town, and residents on the north side can find themselves flooded in or worse, marooned on the wrong side, unable to get home.
As shown in the dashcam footage below, water was well over the bridge and debris was piling up beside it as the cars continued to race across.
Meanwhile, council workers were scrambling to get their 'Bridge Closed' signs up.
Stay up to date: Major flooding predicted into early Saturday morning for Hastings
Bellingen SES Unit Commander Strider Duerinckx said the river rose surprisingly fast.
"It came up really, really quickly and I think council got caught out," he said. "Normally it's not that steep a rise."
He noted that flood management in Bellingen suffered from poor data collection ability upstream.
"The only flood river gauges that we have are at Thora bridge and at Gleniffer. So we're relying on that but there are other creeks that feed in apart from those.
"For example, Rosewood Creek is a big provider of water but we can't graph it.
"And we don't have any rainfall gauges at all. It's pretty hard. The SES is flying fairly blind."
The SES is flying fairly blind.Unit Commander Strider Duerinckx
Asked about Kombu's weather station, which does report rainfall in real time, Strider said that was quite specific to the Bellingen CBD area.
"It's of limited use in terms of what's going on up river," he said.
In their latest bulletin, the BOM said the Bellinger River at Bellingen is expected to peak near 6.7 metres around 2pm today with moderate flooding. Further rises are possible.
The Bellinger River at Repton may peak near the minor flood level (2m) at around 4pm Friday. Further rises are possible.
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