By Helen Chernikoff

NEW YORK, April 2 (Reuters) - Prices of existing Manhattan apartments fell by double digits in the first quarter, according to several market reports released on Thursday by New York City's biggest real estate brokerages.

The median resale price of an existing Manhattan apartment fell 11 percent to $749,000 in the first quarter, according to a report from PropertyShark.com, a foreclosure data Website and The Corcoran Group, New York City's largest brokerage.

"Prices still have downward pressure on them, and you'll see lower prices in the next quarter than you're seeing now," said Corcoran Chief Executive Pam Liebman.

Of all listings in the quarter, 37 percent, or 5,641, saw price cuts, while prices rose on only 136 properties, according to data from real estate Website StreetEasy.com.

The price declines reflect the ongoing turmoil afflicting Wall Street which started in the summer of 2007 with the first stirrings of the credit crisis and intensified last September with Lehman Brothers' bankruptcy, said Gregory Heym, chief economist of brokerage Brown Harris Stevens.

"Wall Street is the leading economic force in the city, so it's not surprising," Heym said.

Brown Harris Stevens' data had median resale prices down by 16 percent in the first quarter.

Job losses and deep cuts in the financial services industry have cooled the normally overheated New York City property market.