The company posted an underlying attributable profit of US$3.7 billion, down 8% on the previous corresponding period and lower than Macquarie's forecast of close to $4 billion.

Underlying EBITDA was $10.5 billion, above Macquarie's estimate of $10.3 billion, while the EBITDA margin from continuing operations was 52%.

Net operating cashflow was $6.7 billion, while free cashflow of $3.6 billion was above the forecast $2.8 billion.

BHP said its productivity guidance was expected to be broadly flat for the full year due to unplanned outages at Olympic Dam, Western Australian Iron Ore, Spence and Nickel West, down from the previous guidance of $1 billion.

BHP previously flagged the copper plant outages, Nickel West fire and iron ore train derailment had a total negative impact of around $600 million.

The final impact to the bottom line was $460 million, reflecting a negative impact of $835 million, which was partially offset by build-up of inventory levels during the outages.

Net debt fell to $9.9 billion, down $1 billion and below Macquarie's estimate of $10.2 billion.

The company declared a 55c per share dividend, above the forecast 52c, unchanged from last year.

"Our focus on portfolio simplification, cash generation and capital discipline delivered higher cash returns to shareholders in the December 2018 half year," BHP CEO Andrew Mackenzie said.

"Our strong balance sheet and fully funded capital investment plans allowed us to return the $10.4 billion net Onshore US proceeds to shareholders in the form of a $5.2 billion off-market share buy-back completed in December 2018 and a $5.2 billion special dividend paid in January 2019."

When adding in today's dividend, it equates to a payout ratio of 75%.

"Since the beginning of 2016, we have reduced debt by $16 billion, reinvested $20 billion in the business and returned more than $25 billion to shareholders," Mackenzie said.

"A strong second half is expected to partially offset the impacts from operational outages in the first half, with unit costs across our business forecast to improve.

"We are confident in our plans to increase shareholder value and returns."

BHP will hold a series of media and investor briefings later today.