UPDATE 3-Best Buy says strong sales not 'new normal,' shares skid

(Adds CEO comment from earnings call)

Aug 29 (Reuters) - Best Buy Co Inc, the No. 1 U.S. consumer electronics retailer, reported a much stronger than expected rise in quarterly same-store sales on Tuesday, but warned that the performance should not be seen as a "new normal."

The company's shares, which jumped more than 5 percent before the bell, fell 8.5 percent in early trading. The stock has gained 46 percent so far this year and last week hit a multi-year high.

Best Buy's sales at established stores rose 5.4 percent in the second quarter ended July 29, handily beating analysts' average expectation for a 2.1 percent increase, according to Consensus Metrix. Sales were driven by wearable devices, laptops and gaming consoles.

But Chief Executive Hubert Joly said on a call with analysts that he did not believe that the mid-single-digit rise in comparable sales would continue.

Best Buy, which was struggling with declining sales and profits as recently as 2015, has tried to turn itself around by closing underperforming stores, improving customer service and most importantly, matching Amazon.com Inc's low prices.

Joly's remarks, however, raised concerns whether that turnaround was sustainable as competition from Amazon intensifies.

Best Buy's sales have beaten analysts' estimates in six of the past eight quarters, a performance unmatched by other electronics retailers such as hhgregg and RadioShack, which went bankrupt.

Online comparable sales in the United States surged about 31 percent, on top of a 23.7 percent increase last year, as faster shipping and improvements to Best Buy's checkout and search functions drew more shoppers.

The company also lifted its annual revenue forecast. Best Buy now expects full-year revenue to rise about 4 percent, compared with an earlier forecast for a 2.5 percent increase.

Asked by analysts about Hurricane Harvey's impact on the forecast, Chief Financial Officer Corie Barry said it was "nearly impossible" to predict the impact at this stage.

Excluding one-time items, Best Buy earned 69 cents per share, beating analysts' estimates of 63 cents, according to Thomson Reuters I/B/E/S.

Net sales climbed 4.8 percent to $8.94 billion. Analysts had expected $8.66 billion. (Reporting by Vibhuti Sharma in Bengaluru; Editing by Sai Sachin Ravikumar)