True horror of September 11 terror attacks revealed in 15 photos we should never forget
On this day 18 years ago, unimaginable horror struck America when four commercial flights were hijacked by terrorists and crashed into sites including New York City's Twin Towers.
The morning of Tuesday, September 11 was fine and sunny, with New Yorkers navigating the manic rush-hour commute to work or school under a cloudless blue sky.
But at 8.46am the unthinkable happened: American Airlines Flight 11, bound for Los Angeles, was hijacked by members of Al-Qaeda at Boston airport and flown into the North Tower of the World Trade Centre.
People stared up in confusion and disbelief at the smoking building, wondering if perhaps it was an accident, until 17 minutes later a second plane, United Airlines Flight 175, hit the South Tower at 9.03am.
By 10.30am the Twin Towers had collapsed, sending people running for their lives covered in dust and debris. Meanwhile, 370 kilometres away, American Airlines Flight 77 was flown into the Pentagon building in Virginia at 9.37am, and United Airlines Flight 93 was crashed into a field near Shanksville, Pennsylvania, at 10.03am.
In less than two hours, 2996 people had been killed and more than 6000 injured, including hundreds of firefighters and police officers who rushed to the scenes.