Can I buy travel insurance for only the first part of my trip as I am already covered for the second part?

Yes, provided you intend to return to Australia.

The return date on your policy should be the date that your other policy starts.

You are not eligible for a policy if you are relocating permanently overseas.
Cover under all policy benefits ends on the return date as specified on your certificate of insurance. There is no cover for any events that occur after the return date as specified on your certificate of insurance, even if the event occurred during your period of insurance with us.

Cover is subject to the policy terms, conditions, limits and exclusions in the Product Disclosure Statement (PDS).