Fitch fears massive European CMBS refinancing risk

* Continental CMBS potentially more risky than UK CMBS

* Sees further value declines clashing with maturity dates

LONDON, Nov 25 (Reuters) - A slower correction in mainland European property values has turned tens of billions of euros of mortgage-backed bonds into potential time-bombs with a greater risk of defaulting than their UK peers, Fitch Ratings said.

The agency has so far this year downgraded 47.2 billion euros ($70.4 billion), or 69 percent, of European CMBS notes it tracks, and maintains either Rating Watch Negative or Negative Outlook on a further 52 billion euros of notes.

It said refinancing risk for commercial mortgage-backed securities (CMBS) linked to French, Dutch or German real estate may be even greater than in Britain because so many transactions were completed at the peak of a property boom in 2006 and 2007.

UK real estate prices have rallied after falling almost 45 percent in the two years to September, but Fitch Senior Director Euan Gatfield said continental European markets may be lagging, with further declines likely to collide with a wave of impending maturities over the next five years.

"There is hope that the worst is over for UK commercial real estate, something that cannot be said for most mainland European markets," Gatfield said.

"With a prolonged wave of maturities arriving in two years time, financing pressures are building in the sector," he said.