There are "no indications" that an 11-alarm blaze that destroyed a Delanco warehouse was set, the township fire chief said Wednesday.

Ron Holt said investigators were working to determine the cause of the blaze at the Dietz & Watson facility. Flames were reported coming from the roof around 1:45 p.m. Sunday, and the fire was brought under control by about 5:40 p.m. Monday.

Holt said a fire suppression team wrapped up early Wednesday afternoon, but a crew would monitor the building overnight. He said two to three minor hot spots remained, but firefighters cannot get to them until Dietz & Watson gets a permit to demolish the building.

A portion of the building that was untouched by the fire is unsafe, Holt said.

Steve Riley, a Dietz & Watson spokesman, said the company was waiting to learn about the cause and whether the building was safe to be demolished.

Delanco officials said the company would have to submit a demolition plan to begin the process, as is the common practice.

Holt said the agencies involved in the investigation include the New Jersey State Police Arson and Bomb Unit, along with the state and county fire marshal's offices, the federal Bureau of Alcohol, Tobacco, Firearms, and Explosives, and Delanco fire officials. The ATF is involved because of the fire's magnitude, Holt said.

Concerns over firefighters' safety due to numerous solar panel units on the roof hindered firefighting, Holt said. Firefighters did not cut portions of the roof because of the possibility of being shocked, he said.

"I'm not risking one of my guys' life for a building," he said.

Holt said up to 300 firefighters from 60 to 70 companies were at the scene. He called it the worst blaze he has fought in his 35-year career.

Dietz & Watson opened the site in 2007.

The company's Philadelphia facility has now assumed a major role in distribution.

"The family is very serious about their employees. They're needed more than ever," Riley said.

Contact Darran Simon at 856-779-3829, or dsimon@phillynews.com, or follow on Twitter @darransimon