A woman wipes away tears as she holds a photograph of Alex Ciccone, a victim of the September 11, 2001 attacks on the World Trade Center, at the National 9/11 Memorial and Museum during ceremonies marking the 16th anniversary of the attacks in New York, US, September 11, 2017. [Photo/Agencies]

While many Americans commemorated this day with tears and wishes, some were worried that as the memory of the tragedy is fading out, similar disastrous incident could happen to the country again.

"I feel like some people have forgotten," Damron Wilson, a volunteer for the commemoration, told Xinhua.

He worried that the American society has "learnt to relax and move on," especially the younger generation.

For Wilson, his feeling of insecurity has worsened when he found that the nation has never been more divided.

"My mum told me that the country had been united after 9/11, but it is deeply divided now. Even today I can see Donald Trump's supporters clashing with people who are against him," he said.

"And with what happened in Charlottesville, I think domestic terrorism is likely to happen (again)," he added.

Last month, violent clashes erupted in Charlottesville, a historic college town in the US state of Virginia, between white nationalists and counterprotesters, leaving one killed and 19 others wounded.

Born and Raised in New York City, Gonel said that he did not feel safe either, especially amid the growing tensions between the city government and the police department.

Staring at the new World Trade Center complex that opened in 2015, Gonel said he was afraid that the center has become more of a tourist spot than a memorial.

"Americans should come here and show some respect. Once you forget, it may happen again," he said.