Dec 31 (Reuters) - Australian shares are set to drop at the open on Friday, as investors turn cautious on the final day of the year after daily coronavirus cases in the country topped 20,000 on Thursday for the first time in the pandemic. The local share price index futures dipped 0.1%, an 85.4-point discount to the underlying S&P/ASX 200 index (.AXJO) close. The benchmark edged up 0.05%, its highest close since Sept. 7, on Thursday. New Zealand"s benchmark S&P/NZX 50 index (.NZ50) rose 0.1% in early trading.