As “John Doe” said, there were Hatzolah ambulances and many Hatzolah members active in lower Manhattan on 9/11.
At least one ambulance was destroyed by the collapsing towers.
A Google search for “Hatzolah 9/11” will bring up some of the chilling pictures taken that day.
It was only due to chasdei H-shem that no Hatzolah members lost their lives.