At least six people have been hospitalised during this morning's Auckland Marathon.

One person was initially described as being in a critical condition, but their condition had since improved. Three people were in a serious condition, St John says.

Race organiser say they can "confirm at this point that during the Auckland Marathon today, six participants have been transported to a nearby hospital where they are receiving medical treatment. We have no further details at this time on the six (unrelated) incidents and will continue to offer the athletes our support."

A half-marathon competitor said she saw three people collapse during her run.

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"I saw people lying on the ground being helped by medics at 3 different spots on the track.

"It looked like one woman had collapsed just past the highest point of the harbour bridge - she was being helped onto a stretcher by St John ambulance staff," she said.

Runners go through a water station at the ASB Auckland Marathon. Photo / Dean Purcell
Runners go through a water station at the ASB Auckland Marathon. Photo / Dean Purcell

"Another man, who looked quite young, was being stretchered away from the track just 3km from the finish line. He was as white as a ghost."

One person collapsed on the harbour bridge.

An image on social media shows just how hard completing a marathon is.