where does the term no worries come from
It is an Australian English expression.
No worries
"No worries" is an Australian English expression, meaning "do not worry about that", or "that's all right". 
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No worries [SEP] Definition
"No worries" is an Australian English expression, meaning "do not worry about that", or "that's all right". It can also mean "sure thing" and "you're welcome". Other colloquial Australian terms which mean the same thing include "she'll be right". The expression has been compared to the American English equivalent "no problem". In their book "Australian Language & Culture: No Worries!", authors Vanessa Battersby, Paul Smitz and Barry Blake note: "No worries is a popular Australian response akin to 'no problems', 'that's OK' or 'sure thing'."