By Sameer Manekar and Shashwat Awasthi

(Reuters) - Australian iron ore miners Rio Tinto and Fortescue Metals Group Ltd are unlikely to see a repeat of record profits booked in recent years as they face soaring costs, falling prices and a tight labour market.

Rio Tinto, the world's biggest iron ore producer, may see its first-half earnings drop by about a third, while Fortescue could report up to a 40% drop in annual profit, according to Refinitiv estimates.

A persistent downward trend in iron ore prices is expected to weigh significantly on earnings of top Australian miners, UBS analyst Lachlan Shaw said.

"When high or rising costs near term are overlaid, earnings momentum will slow further, especially in second-half of 2022 or full-year 2022."

A rebound in iron ore prices from pandemic lows powered miners' profits and shareholder returns in 2021, but a resurgence of COVID-19 curbs and a deepening crisis in China's real estate sector has hit demand outlook this year.

The impact from a dearth of skilled labour in resource-rich Western Australia state and surging global inflation will also likely subdue results this cycle.

China's plan to centralise iron ore purchases has also cast doubt on prospects of global mining giants.

However, full-year earnings at BHP Group, the world's biggest listed miner, are expected to jump 30%, partly benefiting from exposure to a variety of commodities including coal, whose prices have rocketed during the Ukraine conflict.

Rio and BHP's profits nearly doubled from 2019 levels in 2021, while Fortescue's earnings have more than tripled over the past two years.

Lower earnings are expected to lead to reduced returns as payout ratios typically target a percentage of free cash flow paid out to shareholders, UBS' Shaw said.

Rio Tinto will report half-year results on July 27, while BHP and Fortescue will report fiscal 2022 results on Aug. 16 and 29.

(Reporting by Sameer Manekar and Shashwat Awasthi in Bengaluru; Editing by Shounak Dasgupta)