The Notre Dame Cathedral is undergoing repairs in Paris, France, Aug. 16, 2019. The Notre Dame Cathedral in central Paris caught fire on April 15 this year. (Photos: Xinhua/Gao Jing)

The Notre Dame Cathedral is undergoing repairs in Paris, France, Aug. 16, 2019. The Notre Dame Cathedral in central Paris caught fire on April 15 this year.

The Notre Dame Cathedral is undergoing repairs in Paris, France, Aug. 16, 2019. The Notre Dame Cathedral in central Paris caught fire on April 15 this year.

The Notre Dame Cathedral is undergoing repairs in Paris, France, Aug. 16, 2019. The Notre Dame Cathedral in central Paris caught fire on April 15 this year.

The Notre Dame Cathedral is undergoing repairs in Paris, France, Aug. 16, 2019. The Notre Dame Cathedral in central Paris caught fire on April 15 this year.

People view the Notre Dame Cathedral under repairs in Paris, France, Aug.16, 2019. The Notre Dame Cathedral in central Paris caught fire on April 15 this year.

People walk past the Notre Dame Cathedral under repairs in Paris, France, Aug.16, 2019. The Notre Dame Cathedral in central Paris caught fire on April 15 this year.