TRACY, Calif. (AP) — Officials in a Northern California city urged people sensitive to smoke to keep indoors as firefighters spent a third day Saturday battling a fire in a huge medical equipment warehouse.

Air quality on the south side of Tracy, a city of 100,000 people where the Medline warehouse fire has been burning since Thursday, was in the “unhealthy” range, according to air monitors.

Firefighters expected the next few days to remain smoky amid a lengthy effort to put out the fire inside the building, South San Joaquin County Fire Authority Fire Chief Randall Bradley said in a statement.

The local fire marshal was investigating, and officials are meeting with company representatives, structural engineers and others to assess the building, Bradley said.

Plans were being made for employees to retrieve their vehicles from the site. Meanwhile, firefighters urged people to avoid the area and not touch or move debris from the fire.

Medline is a major provider of medical-surgical products such as latex gloves, masks and surgical instruments.

The blaze at the 1 million-square-foot (93,000-square-meter) warehouse about 55 miles (88.5 kilometers) east of San Francisco sent embers flying for miles.

Poorly functioning sprinklers and hydrants with little to no flow hindered firefighter efforts. The problem appeared to be with the facility’s fire-suppression system and not city water supplies, they said.

No issues were found when an outside company tested the sprinkler system in January, firefighters said.