Tonga volcano eruption and tsunami: Shockwave recorded in Tauranga Harbour

The shockwave was recorded by monitoring instruments at Ōmokoroa wharf, pictured in 2018. Photo / Supplied WBOPDC

Live monitoring sites picked up the exact time the shockwave from the Tongan eruption hit Tauranga Harbour.

The Bay of Plenty Regional Council says monitoring sites also recorded evidence of tsunami waves in the Bay of Plenty.

The eruption had occurred roughly between 5.20pm and 5.28pm last Saturday, New Zealand time, the council said in a statement.

The council's monitoring site at Ōmokoroa Wharf in Tauranga Harbour showed a distinct spike in atmospheric pressure from 7.15pm to 8pm as the shockwave from the eruption passed through the area.

Many residents took to social media reporting they heard loud booms, which some believed to be from the eruption.

This was followed by evidence of tsunami waves in the harbour from 9.20pm, with a peak from 1am to 2am on Sunday.

Council data services manager Glenn Ellery said the effects of the tsunami waves were seen in the region's rivers as well as the harbour.

The monitoring site at Ford's Cut on the Kaituna River recorded evidence of tsunami wave action from around 8.45pm on Saturday.

There was a 650mm water level change between 4.38am and 4.59am on Sunday morning.

Ellery said this rapid change in levels represented a significant amount of water, and velocity, surging up the river and an equally strong current flowing out again from the tsunami waves.

"This data shows why it is so important to heed advice from Civil Defence during events such as this," he said.

"Strong and unusual currents and unpredictable surges around our coastlines and river mouths can occur in response to natural events and may not always be easily seen to the eye.

"While we had peak tsunami waves occur early in the morning in this case, when it is unlikely people will be near or in the water, had it occurred at another time we could have swimmers and fishermen easily get into trouble."

Similar results with rapid changes in water levels were seen in monitoring sites from the Western Bay across to the Eastern Bay of Plenty.

The council manages more than 75 live water level monitoring sites across the Bay of Plenty.