* FTSE 100 down 0.6 pct
* Miners weigh after BHP warns about China demand
* Arm boosted by upgrades
By Francesco Canepa
LONDON, March 20 (Reuters) - Britain's top share index was lower on Tuesday morning, weighed down by mining stocks which fell in response to signs of a demand slowdown in China, the world's largest consumer of metals.
Miners fell 2.1 percent after BHP Billiton, the world's biggest miner, said it was seeing evidence of "flattening" iron ore demand from China, which cut its economic growth goal for this year earlier this month.
Shares in BHP and rival Rio Tinto were down 2 percent and 2.7 percent, respectively, having traded 20.4 percent and 30.6 percent of their volume average.
"JPMorgan is not looking for a hard landing in China, but economic activity will remain mixed and will continue softening in the near term," said Emmanuel Cau, JPMorgan European equity strategist said.
"If you look at housing activity in particular, or steel and cement production, they are quite weak at present and we think this is advocating a more cautious view on the mining sector."
Cau, however, was still optimistic on the broader market's long-term prospects, expecting growth in the United States to offset weakness in China and an improvement in company earnings to drive European shares higher.
"Given the macro pick-up we have seen, there is room for earnings upgrades and that's what going to drive the next leg of the rally," he said.
Of the 73 British blue chips that had reported full-year results to date, 64 percent had beaten or met consensus estimates, Thomson Reuters Starmine data showed.
The FTSE 100 fell 33.83 points, or 0.6 percent, to 5,927.18 by 0922 GMT, retreating further from an eight-month closing high of 5,965.58 on Friday.
The index still enjoyed strong technical support and was seen as merely experiencing a temporary pullback before heading towards last year's highs in the 6,100 region, according Cheuvreux.
"We do not exclude (an) addition(al) congestion phase before renewing strength towards the prior swing tops within the 6,050-6,100 target window," the broker said in a note.
"The rising 50-day moving average would act as a strong support, currently at the 5,835 level."
Chip designer ARM Holdings was among the top FTSE risers adding 1.2 percent. The company's recent share price weakness despite its strong competitive position prompted upgrades by Barclays Capital and Investec Securities.
"ARM shares performed weakly over the past year as the market digested its prospects in the PC market and earnings momentum slowed," BarCap said in a note, raising its rating on the stock to "overweight" from "equal-weight".
"With continued upside being seen in the smartphone and tablet segments, and ARM retaining its strong position in both despite threats from Intel, we see (circa) 10 percent upside to consensus estimates for 2012/13," it added.
Glencore, down 1.3 percent, was at the centre of traders' interest, having already traded 37 percent of its volume average after a source said a consortium including the commodities giant was close to a deal to buy Viterra Inc , Canada's biggest grain handler.