Firefighters went called to Greenway Polymers, in Telford, just after midday on Monday after waste material at the premises near the M54 went up in flames and smoke.
The building, in Rock Road, Ketley, will now be dismantled by experts in the next few days.
Assistant Chief Fire Officer Dan Quinn, of Shropshire Fire & Rescue Service, said: “Operations continues on site and the building has been deemed as an unsafe structure due to heat and fire damage.
"Our plan over the coming days will be to work with partners to carry out a controlled dismantling of the structure to remove any risk posed to our staff who are continuing to extinguish the fire and any members of the public.”
The brigade also said the blaze could last between seven to 10 days, with a clean-up operation taking months to complete.
Residents and businesses in the area are being advised to keep doors and windows closed due to smoke from the site billowing in the vicinity.
Meanwhile Shropshire Council has now warned that conditions could affect areas businesses west of the Wrekin - in Eaton Constantine, Upper Longwood, Garmston and Leighton.
Environment Agency spokeswoman Linda Parker said: “We have been consulting with the national air quality experts who have made their assessments of the fire. These have been shared with Public Health England.
“We are in regular communication with the Shropshire Fire and Rescue Service and providing their updates to the national air quality team.
“Our professional partners, including Public Health England, have been assessing the air quality in order for them to make their recommendations on public health.”
Six schools which were closed on Wednesday morning due to drifting smoke but have all now reopened.
And the M54, which smoke has been blowing over, is now back open as normal after initial concerns that the entry road at Junction 6 would need to stay shut for a week.
Formerly known as Greenway Waste Recycling site the plant has been at the centre of a long-running campaign to permanently halt operations at the site near a double bend in Waterloo Road over road safety and concerns over bad smells.
Residents of Lawley, Overdale and Ketley held a protest march in 2016 against plans by Greenway to expand the operation. But the business closed in January 2017.
It was expected to reopen in 2018 after new operator Nottinghamshire based Johnson Aggregates and Recycling Limited won permits to increase the amount of waste to be processed, along with permission for 100 lorry movements each despite residents concerns over traffic and smells, but this did not materialise.
Councillor Shaun Davies, leader of Telford & Wrekin Council, said: “As a council we are doing everything we can to ensure the safety of our residents and businesses and committing resources to minimise the impact.
“We’re committed to working with partners on this significant fire that will take time to fully extinguish. Conditions could change at very short notice and we will continue to do all can to keep everyone up to date on the latest developments.”