Los Angeles firefighters are on their sixth day of battling a fire at a massive warehouse near downtown that stores frozen food.

Smoke has billowed from the warehouse, which was covered in solar panels and insulated like a freezer, filling the air surrounding the roughly 500,000-sq-ft (46,450-sq-meter) facility.

The blaze that broke out last Wednesday has been especially challenging for firefighters due to the nature of the facility operated by Michigan-based Lineage in the Boyle Heights neighborhood east of downtown. Firefighters haven’t been able to enter the building and are instead fighting the blaze from outside.

Authorities said a large warehouse fire can typically be put out in a day, but in a cold storage facility, it can take weeks. Jaime Moore, the chief of the Los Angeles fire department, said there are about 85m lbs (38.6m kg) of frozen food stored inside.

Here’s what to know:

What caused the fire?

The cause of the fire has not been determined, Lineage said in a statement on its website.

The company, which provides temperature-controlled warehouse space to food and beverage makers, believes the fire began when subcontractors were working on solar panels on the roof, the statement said.

Lineage is working with fire officials investigating the blaze, the statement said.

Why is it taking so long to put it out?

It will at least take a few more days to extinguish the fire, said Jamie Stewart, a Los Angeles fire department spokesperson.

Fires in cold storage facilities often burn for weeks because their heavily insulated ceilings, roofs and walls make them difficult to extinguish, Stewart said.

Firefighters have not been able to enter the building due to the danger posed by floor-to-ceiling heavy-duty steel rack shelving, he said. They also have been unable to quickly ventilate the roof due to the insulation, which is what they would typically do to release gas and smoke and gain visibility inside a warehouse, he said.

In this case, firefighters have been stripping away exterior walls on certain sides of the building and dousing it with heavy streams of water, he said.

“I don’t know that we’ll ever get firefighters inside because the entire roof has been compromised and it is sitting on top of [those] 65ft towers,” Moore said. “It’s extremely dangerous, and I don’t foresee ever putting our firefighters in that type of danger.”

What is stored at the facility?

The facility, called Big Bear, stores products such as seafood, pork, beef and poultry before they’re shipped to grocery stores and restaurants on the US west coast, Lineage said on its website.

A message sent to Lineage seeking details about the food and the companies affected by it was not immediately returned.

What are the air quality concerns?

Air quality officials said the air around Boyle Heights, a working-class neighborhood, remained very unhealthy on Monday and that particulates in the smoke were also affecting the San Gabriel valley.

The South Coast Air Quality Management District extended a warning about poor air quality until Tuesday afternoon, saying the blaze continues to produce smoke impacting the neighborhood and areas north and east of the fire. The smoke is carrying microscopic particles known as PM2.5 that can penetrate deep into the lungs.

Light winds will also push the smoke in all directions, potentially affecting other parts of metropolitan LA, the district said.

Los Angeles city councilmember Ysabel Jurado, who represents Boyle Heights, said residents want to know what materials and chemicals were in the warehouse, what burned and what is still burning. She said air quality results should include that information and be released in English and Spanish in terms that regular people can understand.

Jurado said families, workers and other local residents are “seeing the smoke and smelling the odors and binding ash and debris near their homes and businesses.

“We still do not have enough clear information about what burned and what may still be burning,” she said.

Residents in the most affected area were told to avoid vigorous physical activity; close all windows, doors and vents; turn off air conditioning; and bring people and pets to an inside room because of the risk of hazardous air. Those who need to go outside in the smoky conditions should wear an N95 or a P100 mask, health officials said.