They're just lights in the background with a long lens (zoomed in) blowing out the focus on the background elements. Street lights when in focus, throw more light than can be captured, but it's confined to a small space. As the light spreads out from blurring the focus, the overdriven light blooms outward making the pretty circle of light you see there. Just frame with a lighted bridge in the background, or some city lights. Shoot for shallow DoF and watch the beautiful blooming in the background.