* BHP biggest boost on Aussie benchmark
* Myer shares up 16 percent
* A2 Milk's NZ shares close 13.7 percent lower (Updates to close)
May 16 (Reuters) - Australian shares posted modest gains on Wednesday supported by bank stocks and miners, while New Zealand shares fell to their lowest in over a week as a2 Milk shares weighed.
The S&P/ASX 200 index .AXJO rose 0.2 percent, or 9.2 points, to 6,107, adding to gains of 0.6 percent on Tuesday.
BHP BHP.AX was the biggest boost to the index, advancing 1.4 percent as iron ore, oil and copper prices rose. IRONORE/ MET/L O/R
Westpac Banking's WBC.AX 0.7 percent rise followed.
Whitehaven Coal WHC.AX was the best performer on the benchmark, surging 7 percent. the ASX All Ordinaries index .AORD , department store chain Myer Holdings MYR.AX was among top two percentage gainers, up 16 percent, despite posting a fall in third-quarter sales. Somasundaram, market portfolio strategist at Blue Ocean Equities, said considering expectations from Myer were low, its assets and value of business along with the recent cold weather in Sydney supported the stock.
Shares of a2 Milk Company, listed on both Australia and New Zealand stock exchanges, were the biggest drags on both benchmark indexes, diving as much as 20 percent before closing 13.7 percent lower in New Zealand. company's revenue forecast for the year of more than a 63 percent rise failed to meet bullish investor expectations. Milk Ltd SML.NZ , which has infant formula supply agreements with a2 Milk, closed 4.2 percent lower. Zealand's benchmark S&P/NZX 50 index .NZ50 closed 1.8 percent or 153.27 points lower at 8,555.51, in its biggest one-day drop since February.
Fletcher Building's FBU.NZ 1.1 percent fall also hurt the index. The company said on Wednesday it would temporarily pay more interest on its borrowings and use funds from a share sale to repay debt in a deal with its lenders aimed at fixing breaches in debt covenants.