(Reuters) - Global miner Rio Tinto (RIO.AX) (RIO.L) on Tuesday lowered its forecast for shipments of iron ore in calendar 2017 by up to 10 million tonnes due to bad weather and ongoing work to modernise its rail haulage lines.

Iron ore shipments were expected at 330 million tonnes, down from an earlier range of 330 million to 340 million tonnes, the world's number two producer of the steel making raw material said in its second-quarter production report.

"Iron ore shipments were impacted by an acceleration in our rail maintenance programme following poor weather in the first quarter," Chief Executive Jean-Sebastien Jacques said.

Second-quarter iron ore shipments from Australia fell 6 percent from a year ago to 77.7 million tonnes, slightly below analysts' forecasts as Rio Tinto transitions to a driverless train network.

First-half shipments totalled 154.3 million tonnes, indicating the company expects to pick up shipments in the remaining two quarters.

Second-quarter production from its Australian mines dipped 1 percent to 79.8 million tonnes against the year-ago period, Rio Tinto said.

In other minerals, Rio Tinto cut its full-year production target for hard coking coal to 7.2–7.8 million tonnes following a 14 percent fall in second-quarter production after a cyclone that swept across its collieries earlier this year.

(Reporting by Shashwat Pradhan in Bengaluru; Editing by Richard Pullin)