Tickets to the Sept. 11 memorial, which is due to open to the public the day after the 10th anniversary this year, are now available through an online reservation system.

More than 11,500 passes were reserved in the first few hours after the system was activated Monday, the organization said.

Timed reservations will be used for the memorial while construction continues on other World Trade Center projects over the next few years. Officials said the tightly-controlled system is designed to manage capacity and the flow of visitors while the site remains an active construction area.

It will “help ensure a safe and solemn experience for all,” Mayor Bloomberg said in a statement.

The online ticketing system opened at 9 a.m. at www.911memorial.org/visitor-passes. Passes are free, but the form allows visitors to make donations when they reserve tickets.

Those who make reservations will receive an email confirmation and instructions to print their passes.

The memorial consists of two reflecting pools that evoke the footprints of the towers, which are each nearly an acre in size. They also feature the largest manmade waterfalls in North America.

The design was selected in 2004 and construction began in 2006.

The names of the victims from the 2001 attacks, along with those who died in the 1993 bombing, will be inscribed in bronze along the borders of the pools.

The memorial is on track to open Sept. 11, but only families and invited dignitaries will be allowed to visit on the 10th anniversary. Ticketed reservations begin the following day.

A separate hotline was established last week for 9/11 family members to reserve their own passes. Families can also reserve online.

Memorial officials are expected to limit the number of visitors to about 1,500 at a time.

Groups of 10 or more are asked to contact [email protected] or call 212-266-5200.