Residents in the vicinity of a fire in Central Levin are advised to keep their windows and doors closed this morning to avoid exposure to potentially toxic smoke. Video / Paul Williams

A fire that completely destroyed a Levin rubbish depot on Sunday morning and threatened to do the same to an iconic bar right next door is being treated as suspicious.

Thick black smoke from Levin Container Rubbish building on Oxford St that was used to store recycled plastic could be seen from Paraparaumu, more than 50km away.

Fire and Emergency New Zealand assistant commander Steve Hudson, who is based in Paraparaumu, was called to the blaze shortly after 6.24am and could see the plume of smoke as he left home.

When he arrived Hudson joined more than 20 firefighters from crews Levin, Ōtaki, Shannon and Waitarere who battled the blaze in shifts from all angles for most of the day, with access from Oxford St and a service lane at the back of the building.

Plumes of thick black smoke continued to belch from the site as the plastic refused to be subdued and continued to reignite despite the best efforts of firefighters, who worked in shifts to manage fatigue.

An aerial appliance from Whanganui arrive shortly before 8am that had an extendible 17m ladder than enabled firefighters to attack the blaze from directly above.

The building, leased from its Levin owners by Levin Container Rubbish, had been uninhabited since a tornado on May 20 ripped off much of the corrugated iron roofing and damaged two huge loading doors that weighed more than 1.5 tonnes.

Electricity to the building was cut after the tornado. Since then it was used only to store recyclable plastic waste, much of which was compressed into large squares.

The pallets of plastic were all highly flammable and proved extremely difficult to put out. A digger was brought in to drag the molten plastic and break it up so that it was unable to reignite.

The last of the flammable plastic was put out late afternoon, around 4pm. The fire had attracted onlookers throughout the day.

Hudson said the adjoining building O'Malleys Bar was in real danger of catching fire for a time and crews were able to save the iconic pub by dousing the threat from inside.

O'Malleys Bar suffered some damage to the south-eastern side of the building where the women's toilets are located, and smoke damage inside.

After working the late shift, proprietor Martin O'Malley arrived on the scene mid-morning and offered non-alcoholic refreshments to firefighters throughout the course of the day.

A FENZ crew from Palmerston North manned the Levin station for the morning and was relieved by an appliance and crew from Paraparaumu that afternoon.

The Levin Container Rubbish site was fenced off and what was left of the building would now be demolished.

FENZ investigators had conducted a scene examination to determine the cause of the fire and police were also involved and had been provided with security video footage.