although a visually stunning city, christchurch is quite dangerous at night. I lived there for four years, and got regularly hassled by groups of drunk young guys (15-20).
the most dangerous areas at night are at the sydenham (pronounced sid-nam) end of colombo st (most cars parked there overnight get damaged, if not all), in and around the city square, the city end of worcester st, and outside the bus exchange in the city. in its first year, the bus exchange averaged, on weekend nights, just short of one assault a day.
there is a 'dry zone' where you may not drink or carry alcohol in public view between the four avenues, so if youve got a traveller beware! oh, and dont go to auckland :P
My bus stop on Ilam Rd at 1.30pm today. Obviously someone had a party here last night. The burnt out area of the image is the heap of broken glass that fell down from the other side of the poster, which is what the vandals had broken. This is actually the 2nd time in one week that someone has broken the glass.
Just a note of caution - if you intend to stay out late and party in the city area, ladies, pls. go out in groups. I personally found it a little scarry when late at nite and walking back to the hostel even I had a friend with me. There are police around sometimes but not all the time.