LONDON, Feb 3 (Reuters) - Billions of dollars in new bets against China’s yuan have been placed on derivatives markets this week as currency dealers weigh the chance of an official devaluation around this month’s G20 finance chiefs’ meeting in Shanghai.

Yuan volatility and the bias towards a weaker yuan in options markets have surged to record highs in the past week and dealers say billions of “low delta puts”, which pay out only when the offshore yuan rate gets above 7.20 per dollar, have been taken out.

The yuan is also back under pressure in the offshore spot market, falling to a three-week low of 6.6510 yuan as London opened on Wednesday. Onshore rates, which China controls tightly, were steady at 6.5778.

One-month volatility on the offshore yuan jumped from below 8 percent to almost 10 percent, a record high, versus 8.5 percent on the euro-dollar equivalent.

Traders said option volumes - difficult to track because most of the market is conducted over-the-counter rather than on traceable platforms or exchanges - reached $12 billion on Monday and almost $17 billion on Tuesday.

In morning trade in London, when dealers in the world’s biggest currency trading centre are operating alongside their counterparts in Beijing and Shanghai, the bias toward a weaker yuan - essentially a net measurement - on 1-, 2-, 3- and 6-month contracts all surpassed record levels hit in August.

“Clearly, the market sees that the intensive intervention from PBoC (People’s Bank of China) is not sustainable, and therefore the central bank will have to let the currency go at some point,” said Hao Zhou, a currency strategist at Commerzbank in Singapore.

Much talk centres around how much more China will have leaked in reserves in January, in data due by the end of this week.

Reuters polling of more than a dozen banks puts the fall at a record $130 billion, reducing China’s warchest to combat yuan weakness to $3.2 trillion.

Some hedge funds betting against the yuan have speculated the drop will be $200 billion or more. The sales desk of one large international bank in London was circulating an estimate of $262 billion to selected clients on Tuesday in an email seen by Reuters.

WARNINGS

Analysts from Bank of America Merrill Lynch called on Friday for G20 financial leaders to agree next month in Shanghai to joint steps that would include a one-off devaluation of the yuan and a commitment to a stable dollar to prop up flagging growth and head off another financial market panic.

Against that, China has repeatedly warned “speculators” in the run up to the week-long Lunar New Year starting this weekend that it will keep the yuan steady.

China launches its 12-month presidency of the G20 group of developed and developing economies with the Shanghai meeting of finance ministers and central bank governors on Feb. 26-27.

Another big report this week on the yuan, from analysts at French bank Societe Generale, gave a one-in-three probability of the currency sliding to 7.50 by the end of 2016.

“The People’s Bank of China (PBoC) may insist that it has no intention to devalue the yuan, but capital flows are putting significant downward pressure on the currency. China’s FX reserves are large but far from unlimited, or even sufficient, if large capital outflows persist.

“Our central scenario (65 percent probability) envisions USD/CNY reaching 6.80 in 2016 in a largely gradual and controlled manner, but there is a large and growing risk that USD/CNY trades up to 7.50 this year.” (Editing by Ruth Pitchford)