Paramedics are treating a person in a critical condition after a "water-related incident" at a North Island waterfall beauty spot this afternoon. 

Police and Fire and Emergency New Zealand got calls just before 2.45pm of a "water-related incident" at the Mangamate Waterfall on the Whirinaki River – inland from Minginui in the Ureweras. 

Fire crews and a helicopter are at the remote scene. 

A police spokesman said the incident was "still unfolding". 

A spokeswoman for St John said they were alerted at 2.37pm and sent one first response unit, a helicopter, three ambulances and a manager. 

It was later confirmed that one person in a critical condition was being treated at the scene. 

More information will follow. 

Meanwhile, the search for a missing swimmer last seen entering the Waikato River is ongoing. 

The man was last seen just after 6pm on Monday jumping into the water from or near the jetty at Hamilton Gardens. 

The man went missing at the Waikato River on Monday. Photo / File 

Initial reports to police indicated that a group of four people had gone into the river but only three had come back to shore. 

It sparked a massive search and rescue effort down river towards Claudelands Bridge over the last few days, including the Westpac Rescue Helicopter, boat, jet ski, and police national dive squad. 

This afternoon, police said the dive squad was still searching the section of the river through the Hamilton Gardens and "downstream of that". The police boat has also been helping the search today. 

It has been the worst summer so far for drownings in New Zealand since 2015, according to Water Safety New Zealand. 

As of January 3, there had been 22 drownings across the country since the beginning of December, with another two months to go before the end of the summer reporting period. 

Last summer, 25 drownings were recorded across the whole three-month period, which is also the average over the past five summers. 

Water Safety New Zealand chief executive Daniel Gerrard said the uptick in fatalities was "unprecedented". 

"We have to start making some of these calls ... this is the worst we've had the last six years," he said. 

"We're up to 22 and we've still got two months to go ... last year was 25 total so there's absolute alarm bells." 

- by Kurt Bayer, NZ Herald