SYDNEY (Reuters) - BHP Billiton (>> BHP Billiton Limited) (>> BHP Billiton plc), the world's biggest diversified miner, said on Wednesday it was finally detecting indications of a commodity market turnaround, giving its most upbeat assessment in about five years.

A recovery would be a particular boon for the global miner which has kept production humming through a multi-year collapse in commodities markets, although it cautioned that raw material supply was still outpacing demand despite stronger steel consumption in China.

"We have seen early signs of markets rebalancing," Chief Executive Andrew Mackenzie said in releasing BHP's September quarter production report and guidance update.

"Fundamentals suggest both oil and gas markets will improve over the next 12 to 18 months. Iron ore and metallurgical coal prices have been stronger than expected, although we continue to expect supply to grow more quickly than demand in the near term," he said.

BHP beat analysts' estimates for iron ore and petroleum production and just missed projections for output of metallurgical coal - three commodities leading the resurgence.

"This is probably the most positive assessment by BHP in five years," James Wilson, an analyst for Argonaut Securities, said.

Most forecasters earlier in the year were calling for Chinese steel production and consumption to contract as its economy recoils, prolonging the pain for mining companies like BHP.

Morgan Stanley estimates that China's implied apparent steel consumption in September rose 12.5 percent from a year ago and 2.8 percent from the previous month. That is good news for mining companies looking to China to turn around otherwise sluggish demand.

China's iron ore imports climbed to 93 million tonnes in September, the second highest on record. Spot iron ore <.IO62-CNI=SI> last stood at $58 a tonne, the highest in over a month.

Metallurgical coal prices have more than doubled since January to around $230 a tonne, while nickel has gained 16 percent.

BHP said it was on track to meet its fiscal 2017 production guidance for iron ore of 265 million to 275 million tonnes versus 257 million last year after posting a modest 1 percent decline in output to 67 million tonnes in the September quarter.

Guidance for copper production was under review following a power disruption this month at the Olympic Dam mine, but otherwise BHP stuck with earlier estimates for its other businesses.

Fellow Australian miners Rio Tinto (>> Rio Tinto Limited) (>> Rio Tinto plc) and Fortescue Metals Group (>> Fortescue Metals Group Limited) are scheduled to release operations data and updated guidance on Thursday and are also expected to deliver more upbeat business outlooks.

(Reporting by James Regan; Editing by Richard Pullin)

By James Regan