The devastating fire that consumed the Notre Dame Cathedral in April spread toxic dust over Paris — exposing at least 6,000 children under the age of six to alarming levels of lead, according to a new report.

French authorities were alerted that lead exposure could be a problem within 48 hours of the April 15 blaze — but it took a month before city officials conducted the first test, a New York Times investigation published Saturday found.

More than 450 tons of lead that had covered the Gothic gem’s roof and iconic spire dispersed as dust during the inferno, settling in schools, day cares, parks and other public places, according to the report.

“It’s almost a no-brainer that if you incinerate hundreds of tons of lead, you’re going to have some significant deposition of particles in the neighborhood,” Matthew J. Chachère, counsel to the New York City Coalition to End Lead Poisoning, told the paper.

Confidential documents obtained by the Times found that lead deposited near the historic house of worship were up to 1,300 times higher than French safety guidelines.

The Culture Ministry reportedly waited four months to finish a full decontamination of the neighborhood and failed to enforce safety guidelines for workers, leaving them exposed to dangerous levels of lead.

Tests revealed that at least 18 schools and day cares in the area had unsafe levels of lead and dozens of public places had 60 times the acceptable levels of lead.

Hundreds of kids continued to go to school before testing and clean-up efforts began, the Times reported.

The lead issue wasn’t communicated to the public openly because “the state was afraid to make people afraid,” said Anne Souyris, the city’s deputy mayor in charge of health.

“They thought that they would protect people by not communicating about the lead issue,” she added.

Some health experts consulted by the paper warned against taking small children near the cathedral.

Others said not all the high levels of toxicity could be attributed to the fire and that they could reflect a broader problem in the old city’s infrastructure.