Fire and Emergency NZ crews responded to the blaze this afternoon between the Fernhill township and the Ngaruroro River bridge on State Highway 50.
St John said one person has been taken to hospital in a serious condition, and another ambulance and a rapid response vehicle were at the scene on standby.
Fire crews had ordered some evacuations for residents living near the Farmhouse Lodge on the outskirts of Fernhill.
Everyone living around the lodge had been accounted for, a spokesperson said.
Hawke's Bay Fire and Emergency said conditions were too windy for air operations, but five trucks, three tankers and support vehicles were working to contain the fire. It was about 400m by 200m in size at 2.30pm.
People in the area should stay indoors and keep windows and doors shut to avoid smoke exposure.
Police said a section the state highway has been closed and would remain so for some time due to smoke compromising visibility.
The public should avoid the area and take alternate routes or expect delays.
Havelock North blaze
Meanwhile, crews were also working on another scrub fire threatening houses near Havelock North, but it was contained at this stage.
A Fire and Emergency spokesperson said the blaze was threatening houses, but there were no formal evacuations at this stage. However, nearby residents had been told to leave if they felt unsafe.
Hastings mayor Wendy Schollum said her heartfelt sympathy went to everyone affected.
"It's a really distressing time of year for our community to be facing something like this."
Schollum said the blaze emphasised the importance of adhering to fire bans, with record high temperatures last month, compounded by high winds.
"While we had a little bit of rain more recently, it's not enough to make a meaningful difference.
"That complete fire ban is something we need our community to take seriously, and that includes things like fireworks too ... if you've tucked some away from earlier in the year, please don't set them off."
Multiple fire restrictions were in place in Hawke's Bay, with crews warning of high fire danger levels.
