More than a week after a fire tore through a 116-year-old building in Portland, Ore., what remains of the badly damaged warehouse is causing disruptions and frustrating city officials.

The old Centennial Mills building, a former flour mill, sits a half-mile from Portland’s Union Station and abuts railroad tracks. When it went up in flames on Aug. 2, every floor of the eight-story warehouse collapsed. The cause of the blaze remains under investigation.

“A safety perimeter has been set up around the site to keep the public away from the potential collapse zone,” Dan Douthit, a spokesman for the city of Portland, said in an email. He added that the fire had gutted the building.

The city ordered the building’s owner to demolish it by Aug. 14, but the need for specialized engineers and equipment has complicated those efforts. “The building is too dangerous for even our investigators to be near or inside it,” Lauren Johnson, the city’s fire chief, said at a news conference on Monday.

Amtrak train service between Portland and Seattle has been suspended since the fire. The building is near railway tracks and bounded by the Willamette River, and officials are worried that the rumbling of a passing train could shake the building enough to bring it down. A safety zone has been established around the building, and a nearby park has been closed.

But Union Pacific, a freight transportation company, resumed operations on Tuesday in a decision city officials called a “significant risk to health and safety.”

A spokeswoman for Union Pacific, Robynn Tysver, said in an email statement that the transportation company was operating, but with limits. Its trains are running on the track farthest from the structure and traveling under a voluntary speed limit. She said the company was in close contact with the city.

“Union Pacific recognizes the challenges presented by this incident,” Ms. Tysver said in the statement, “but, with no end date on when this long-abandoned property will be demolished, we must consider the disruption the closure of this critical rail corridor has on regional industries, small businesses, ports and consumer goods.”

According to local news reports, Union Pacific did say it would not ship hazardous cargo past the building until Aug. 21.

Portland officials are concerned that the building’s collapse could result in “death or serious injury to those on the train and damage to the surrounding property,” Raymond Lee, the city administrator, said at the Monday news conference.

“We know Portlanders want answers,” he said. “We’re committed to sharing information as it becomes available. But this remains both an active investigation and a dangerous site.”

Amtrak is offering shuttle bus service for some routes, for those who have train tickets, while other routes have been canceled entirely. Customers can rebook or request a full refund at no additional cost, Amtrak said.

The building contained asbestos and possibly other harmful toxins, according to a statement from three investigating agencies, and the city has advised residents on how to more safely clean up ash and debris. The debris from the demolition is another concern the city aims to address.