The chances of anyone finding fragments of the meteor that shot over Canterbury before slamming to earth are astronomically small.

Within hours of yesterday's sonic boom just before 3pm yesterday, caused by the space rock, sellers on TradeMe were offering pieces they claim were the meteorite.

But Andrew Buckingham from Auckland's Stardome Observatory says while the original rock was probably about the size of a large ball, it may have broken into pebble-sized pieces. He says unless it is known where it landed, the chances of finding a piece are tiny as it would look like any other rock in Canterbury.

Mr Buckingham says anyone who suspects they might have a fragment, can get it tested to determine its origin.