* Spot iron ore on course for biggest monthly fall since 2012
* Iron ore stocks at China's ports highest since Dec 2014
* Raw material coke also posts worst month
* But other China commodities, mainly ags, fare better (Adds other China commodities, details, updates prices)
By Manolo Serapio Jr
MANILA, May 31 (Reuters) - Chinese steel and iron ore futures posted their sharpest monthly falls on record in May on weaker seasonal demand, with the industrial raw materials expected to face more pain in June due to rising steel supply in the world's top producer.
May's decline follows a spectacular December to April rally fuelled by optimism about China's economy. The buying intensified last month, swelling prices and volumes across Chinese commodities as a buying frenzy in steel-linked futures spread in everything from cotton to eggs.
But sentiment soured in May as recent indicators from retail sales to trade suggested a solid recovery was not yet in place and after exchanges put in trading curbs. price surge pushed many shuttered Chinese steel mills to resume operations, increasing supply that could keep steel markets under pressure as seasonal demand slows down with hot weather curbing construction activity from June.
These mills "just don't start and stop with the flows of seasonal demand," said Daniel Hynes, senior commodity strategist at ANZ Bank.
"We'd expect those to remain open for the time being and that probably should result in steel production holding up relatively well despite that normal seasonal slowdown."
The most-traded rebar on the Shanghai Futures Exchange SRBcv1 closed 0.8 percent lower at 1,978 yuan ($300) a tonne.
Rebar, or reinforcing steel used in construction, has fallen 29 percent from its April peak. For the month, it lost 23 percent, the most since the Shanghai exchange launched rebar futures in 2009.
On the Dalian Commodity Exchange, the most-active iron ore DCIOcv1 gained 0.3 percent to 344 yuan a tonne. The contract was down 32 percent from April's high and 25 percent over May, its biggest monthly decline since launch in 2013.
AGRICULTURE COMMODITIES GAIN
Stocks of imported iron ore at China's major ports have continued to rise, hitting 100.65 million tonnes on May 27, the highest since December 2014, according to data tracked by industry consultancy SteelHome.
Given Chinese steel production has been holding up, ANZ's Hynes said he did not expect the iron ore port inventory to rise sharply from current levels.
Spot iron ore could find strong support at around $50 a tonne, he said.
Iron ore for immediate delivery to China's Tianjin port .IO62-CNI=SI slipped 1.2 percent to $50.30 a tonne on Monday, data compiled by The Steel Index showed.
The spot benchmark has lost 23 percent so far in May, the biggest monthly drop since August 2012.
Coke, another steelmaking raw material, rose 1.2 percent on Tuesday in Dalian DCJcv1 . Though the contract ended May down 22 percent, also its biggest monthly loss ever.
Other China-traded commodities fared better for the month, with Zhengzhou cotton CCFcv1 up 3 percent, Dalian soymeal DSMcv1 up nearly 11 percent, Dalian corn DCCcv1 rising 6 percent and Zhengzhou rapeseed meal CRSMcv1 gaining 11.4 percent. ($1 = 6.5840 Chinese yuan) (Editing by Tom Hogue and Ed Davies)