Hi Oleg,
Thanks for your response.
However, I'm still doubtful because according to Google, the hreflang tag is mostly used when you have different sub-domains or directories such as es.mysite.com or www.mysite.com/es/ and so on.
In my case, I will have one single website (in English) but with different TLDs like www.mysite.com for the US, www.mysite.co.uk for UK, www.mysite.com.au for Australia. However, Google does no make any mention about the usage of hreflang in this particular case.
What I want is that Google pick up and display the correct TLD according to the user's location but I really fear that duplicate content may be a serious issue. I've by doing research for days and I'm unable to find a relevant answer.