Customers have been left devastated as a massive fire at a Sydney storage facility likely leaves their belongings in ashes as crews continue to battle the blaze.

The blaze broke out at Storage King Moorebank on Governor Macquarie Dr in Chipping Norton just before 2pm on Wednesday.

WATCH THE VIDEO ABOVE: Storage facility fire burns for second night

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About 80 firefighters and 20 fire trucks remained at the scene on Thursday as crews continued to battle the blaze.

Those with possessions and livelihoods inside the facility could only watch it continue to burn.

“It’s pretty devastating running a business out of here. Tools, tools, tools. My trailer, literally everything for my business is in there,” builder Michael Tucker said.

“Sick to the stomach because I know what’s in there and every time I think about it, I think of something else that’s in a box that we’re never going to be able to get back,” teary Kelly Hill said.

“We’ve got family medals in there, history medals, you know, from World War I, World War II.”

Kelly Hill stored belongings at the facility. Credit: 7NEWS

Storage King told 7NEWS.com.au earlier on Thursday that the facility had been heavily impacted and warned customers they may not be able to access their storage units for several days.

“Storage King has contacted all customers to alert them to the fire and let them know that the entire site is closed,” a spokesperson said. 

“Our team does not have access to the site so we can only tell customers what we are told by emergency services and what we can see from the ground and from aerial footage.

“It is very difficult to ascertain when the site will be handed back by emergency services to Storage King, and when it will be safe for customers to gain access, but it is likely to be several days at a minimum. 

“This will be heavily dependent on expert advice about the extent of damage and safety hazards, and any work required to make the site safe.”

It is not yet clear how many storage units have been affected. Credit: 7NEWS

The company said it was too early to determine how many individual storage units had been affected.

“We know this is a stressful time for our customers and that it will take some time to get the level of detail they need right now,” the spokesperson added.

“We appreciate their patience as we gather information about their individual circumstances.”

Storage King said it offers insurance for possessions, with the choice up to customers. However, many at the facility didn’t take out policies. 

“Literally life-saving. I worked hard to get into it. A lot of people in there lost a lot of businesses,” customer and owner of Absolute Showbags Kass Idriss aid.

Two Storage King staff members were on site when the fire broke out and helped customers evacuate safely, the company said.

Witnesses told 7NEWS they heard several explosions before the fire spread rapidly.

Firefighters remained at the scene on Thursday to contain the blaze. Credit: 7NEWS

About 30 people, including workers from neighbouring businesses, were evacuated as the fire spread.

One person was treated for smoke inhalation and taken to hospital.

At the height of the emergency, Fire and Rescue NSW deployed about 130 firefighters and 22 fire trucks to battle the blaze.

By 5.40pm, the complex’s main building had been destroyed.

“It’s a very challenging fire. Our crews are finding the fire is very deep-seated and there’s been some internal structural collapse,” FRNSW Acting Superintendent Steve Brown said.

7NEWS helicopter footage shows thick black smoke billowing into the sky as flames continue to engulf the facility.

Customers were unable to access their belongings after the fire. Credit: FRNSW

The cause of the blaze remains under investigation.

Fire and Rescue NSW urged nearby residents to keep their doors and windows closed because of the toxic smoke, while motorists were advised to avoid the area as road closures remained in place.

Storage King encouraged customers requiring assistance to contact its Customer Care Team on 1800 888 200, saying it would continue providing updates as more information became available.