When Eastown Timber owner James Richardson left home to head to a fire at his factory on the other side of town, he could already see something serious was unfolding.
"When you can see the horizon lit up with the flames from your own business, it's not good," he said.
By 6am on Friday one of the company's buildings was well alight and flames could be seen licking upwards as the fire was threatening to spread.
At the height of the response to the fire there were seven appliances and a command unit set up on the small driveway off Hakeke St leading into Eastown Timber.
Fire trucks came from as far as Palmerston North, Bulls and New Plymouth.
As of 3pm on Friday there were still three appliances there, and diggers were helping to dampen down the remaining embers.
"They did a good job, cut off the fire - we couldn't do a lot with the building that was on fire, we just stopped it from spreading," Fire and Emergency NZ Whanganui group manager Aaron Summerhays said.
"It was well developed on the arrival."
By 7am, crowds started to gather on the streets surrounding Eastown Timber as residents all over the city could see the massive plume of smoke.
That smoke later led to a call from police and fire services for nearby residents to shut windows to stop draughts of it from getting inside.
People were now fine to open their windows as the fire had been put out, Summerhays said.
"If you can smell smoke, keep your windows closed. Just like any by-product that's been burning ... we want to avoid exposure."
An investigation is now under way as to how the fire started and Summerhays said the early stages of that had already begun.
It was too early and too difficult to say if the fire was at all suspicious, he said.
Richardson has vowed his company will go on and its retail operations will resume on Monday unaffected.
He said they had lost a treatment plant, a paint line and a planer.
"We still have a lot of the plant left.
"Retail operations will be unaffected. Retail will be open on Monday and it will be business as usual."
They would now talk to insurers before beginning work on a rebuild, he said.
By mid-morning, on Friday the fire was mostly out and firefighters were dousing the remaining flames.
A crew was staying overnight on Friday to ensure the fire didn't reignite.
The Whanganui East Pool, which sits only a few metres from the destroyed building, appeared to have not been damaged, according to a civil defence responder on the scene.
TÅtara Puku Kindergarten, which is about 500m from Easttown was closed because of concerns around the smoke.
Police blocked off surrounding streets with parts of Tinirau St, Hakeke St, Holyoake St and Eastown Rd all closed.
Trains were suspended as a precaution, KiwiRail said.
"KiwiRail staff worked with Fire and Emergency to lessen the risk to the rail line by cooling it, and the track will be assessed before letting trains through," chief operating officer of rail operations Siva Sivapakkiam said.
There was an ambulance at the scene, but no injuries were reported.
Don Tait lives next door to the Whanganui East Pool, with Eastown Timber on the far side.
He hadn't heard the fire and was woken up by a knock on the door at about 6am.
"I didn't feel it was going to get me, because the pool was next door - unless there were explosions," he said.
- Additional reporting Laurel Stowell