* Euro banks face another 195 bln euros in write-offs -ECB
* ECB discloses increased euro zone sovereign bond buying
* Spain says will reform labour market even without accord
* China says euro zone debt crisis poses global growth risk
(Updates with ECB on euro zone bank write-offs)
By Krista Hughes and Paul Day
FRANKFURT/MADRID, May 31 (Reuters) - The European Central Bank warned on Monday that euro zone banks face up to 195 billion euros in a "second wave" of potential loan losses over the next 18 months due to the financial crisis, and disclosed it had increased purchases of euro zone government bonds.
As the euro recouped losses but remained on the back foot after a cut in Spain's credit rating and China warned that the global economy remained vulnerable to sovereign debt risks, Spain assured investors it would reform its rigid labour market even if employers and trade unions cannot agree.
The ECB said euro zone banks would need to make provisions for further losses this year of 90 billion euros, and 105 billion in 2011, on top of some 238 billion euros in bad debts written off by the end of 2009. That was the first time it has given an estimate for next year.
Although total write-downs from bad loans and securities between 2007 and the end of 2010 were likely to be lower than previously expected, the ECB said in its latest Financial Stability Report, write-downs this year and next year would be still larger if heightened sovereign debt risk and the impact of government belt-tightening dragged down economic growth.
The ECB began buying up mostly Greek, Portuguese and Spanish bonds on May 3 in a contentious move to calm debt markets and support an $1 trillion stabilisation package for the euro agreed by the European Union and the International Monetary Fund.
The central bank said in a statement it had settled 35 billion euros in bond purchases by May 28, up from 26.5 billion a week earlier. It did not detail the nationality of the debt but ECB officials have said it is mostly from south European countries hardest hit by financial market turmoil.
The ECB acknowledged in its report that euro zone debt tensions may force it to delay a phasing-out of cheap lending operations designed to help banks through the financial crisis.
After Lehman Brothers collapsed in September 2008, the ECB began offering euro zone banks unlimited, flate-rate loans in a bid to revive inter-bank lending and keep credit flowing to the real economy.
ECB governing council member Axel Weber, president of Germany's powerful Bundesbank, urged a tight cap on the bond buying programme and said the extraordinary steps taken to ease the euro zone debt crisis posed a risk to price stability.
"The purchases of government bonds in the secondary market should not overshoot a tightly-capped limit," Weber said in a speech prepared for delivery in Mainz, Germany. He did not suggest a figure.
Spain, the fourth-largest euro zone economy, saw its credit rating downgraded a notch by Fitch Ratings agency from the maximum AAA to AA+ late on Friday after a 15 billion euro austerity programme squeaked through parliament by a single vote.
Market reaction to the downgrade was limited, partly because U.S. and British markets were closed for holidays on Monday.
The euro recouped losses incurred after the Spanish debt downgrade to trade at around $1.23 but remained on the back foot as the downgrade highlighted ongoing structural weaknesses in the euro zone. The 10-year Spanish-German bond spread widened only slightly but Spanish stocks fell 0.7 percent while the index of leading European shares gained 0.4 percent.
LABOUR REFORM
Spanish Economy Minister Elena Salgado told a conference in Madrid that the government aimed to pass a much anticipated labour market reform by the end of June with or without consensus with the unions and business representatives.
The minority Socialist administration extended the deadline for an agreement by one week from Monday but officials have said the social partners are still far apart.
The left-leaning daily El Pais said the government planned to allow companies to make greater use of cheap work contracts for a broader range of employees, reducing redundancy payments and making it easier to fire workers.
Trade unions have threatened to strike if the government imposes the reform by royal decree, a move that would set the ruling Socialists on a collision course with their traditional allies in organised labour.
In a sign of continued international concern about the impact of Europe's problems, China warned that Europe's struggle to contain ballooning debt posed a risk to global economic growth, raising the spectre of a double-dip recession.
Premier Wen Jiabao, addressing business leaders during an official visit to Japan, issued his warnings a day after France admitted it would struggle to keep its top credit rating.
"Some countries have experienced sovereign debt crises, for example Greece. Is this kind of phenomenon over? Now it seems that it's not so simple," Wen said. "The sovereign debt crisis in some European countries may drag down Europe's economic recovery."
He added it was too early to wind down stimulus deployed during the 2007-2009 financial crisis.
Governments around the world ran up record debts during the $5 trillion effort to pull the economy out of its deepest slump since the Great Depression and now face a tough balancing act: how to reduce debt without choking off growth.
ECB Governing Council Member Mario Draghi warned that austerity programmes by European governments could snuff out a fragile recovery unless they were coordinated internationally.
Economic sentiment in the euro zone fell in May, defying analysts expectations of a slight improvement, in part due to the wave of austerity announcements.
However, ECB President Jean-Claude Trichet said the economy may expand more than expected in the second quarter.
The fact that not just fiscally weak southern European countries, but also nations such as France and Germany at the euro zone's core are under pressure to cut debt and deficits amassed during the financial crisis, is adding to concerns.
(Additional reporting by Sarah Morris in Madrid, Martin Santa and Sakari Suoninen in Vienna, Marc Jones in Frankfurt; Writing by Paul Taylor; Editing by Ron Askew and Susan Fenton)