LONDON- Healthy demand from stainless steel mills and electric vehicle battery makers is expected to underpin nickel prices over coming months, but rising supplies from top producer Indonesia are likely to weigh next year.

Benchmark nickel prices on the London Metal Exchange, at $19,500 a tonne, are up more than 20% since April and at their highest since February.

A few months ago, expectations had been for surpluses in the second half of this year, but now shortages are more likely.

"This year has seen one of the most remarkable turnarounds in nickel consumption, it has been driven by booming conditions in the stainless steel and battery markets," said Macquarie analyst Jim Lennon.

"But the relentless rise in Indonesian production, combined with an expected slowdown in the pace of nickel consumption growth should tip the market into over-supply in 2022/23."

Macquarie expects demand to rise to 2.8 million tonnes this year, a rise of 16% from 2020, and a deficit of 83,000 tonnes. In March it had predicted nickel demand growth at 10.6%. Production of 300-series stainless steel containing 8%-9% nickel jumped 36% in the first half of 2021 compared with the same period last year.

Stainless accounts for around 70% of global nickel consumption, while electric vehicle batteries consume less than 10%, but the latter number is expected to rise alongside electric vehicle sales as the world moves to cut carbon emissions.

Supplies are under pressure this year due to disruptions at nickel mines in New Caledonia, Russia and Canada. Analysts estimate the market lost around 60,000 tonnes of nickel due to these disruptions.

COVID-related restrictions also raise the possibility of delays to new projects in top producer Indonesia this year.

Citi analyst Oliver Nugent is looking for nickel prices to reach $20,500 over the next three months and cites sliding exchange stocks as a sign of "brewing physical tightness".

Stocks of nickel in London Metal Exchange approved warehouses, at 219,180 tonnes, have fallen more than 15% since April, while those monitored by the Shanghai Futures Exchange are near five-year lows. "We remain directionally bearish in 2022 as we anticipate strong supply growth from Indonesia," Nugent said.

(Reporting by Pratima Desai; Editing by Pravin Char) ((pratima.desai@thomsonreuters.com; +44 207 513 5681;))