FTSE falls into "bear market" territory, miners slump

(Updates with closing prices, details)

* FTSE 100 falls 20 percent since April (LSE: 0N69.L - news) peak

* Commodities-related indexes hit 12-year lows

* BHP Billiton (NYSE: BBL - news) sees no recovery in iron ore prices

By Atul Prakash and Kit Rees

LONDON, Jan 20 (Reuters) - Britain's blue-chip equity index entered "bear market" territory on Wednesday after falling more than 20 percent from its record highs in April, with concerns about China triggering a sharp decline in commodities-related stocks.

The benchmark FTSE 100 index ended 3.5 percent lower at 5,673.58 points after touching 5,639.88, its lowest level in more than three years.

"The FTSE is now in a bear market," said Brenda Kelly, an analyst at London Capital Group. "It (Other OTC: ITGL - news) 's not a pretty sight with every single sector in the red."

Technical analysts define a "bear market" as one in which the index falls more than 20 percent from its previous peak.

The UK mining and energy indexes both slumped 5.6 percent to their lowest levels in about 12 years, with a sharp decline in oil and metals prices scaring investors away from commodities stocks.

Shares (Berlin: DI6.BE - news) in commodities-related companies such as BHP Billiton , Anglo American (LSE: AAL.L - news) , Glencore (Xetra: A1JAGV - news) and Royal Dutch Shell plummeted by between 7.2 percent and 9.9 percent.

Mining and energy stocks have been hit by a slowdown in China, the world's second-biggest economy and a major global consumer of metals and oil.

"We do not see any lasting potential for these sectors to outperform and believe any recovery might be short-lived," said Christian Stocker, equity strategist at UniCredit (EUREX: DE000A163206.EX - news) .

"The trend of earnings estimates is declining strongly, relative valuation versus the overall market is still very high and a lasting trend reversal in commodity prices is not in sight. We recommend remaining underweight on commodity stocks."

BHP Billiton came under further pressure after saying it expected no recovery in iron ore or coal prices in the next few years, with global markets suffering from oversupply and a slowdown in China, the world's biggest metals consumer.

Among mid-caps, pub chain operator J D Wetherspoon (LSE: JDW.L - news) slumped 9.7 percent after warning that 2016 profits would be at the lower end of analysts' expectations. (Additional reporting by Sudip Kar-Gupta; Editing by Ruth Pitchford)