* JB Hi-Fi H1 underlying net profit at record high of A$151.7 mln
* Company warns full-year profit to grow slower than sales
* Shares down 7.8 pct, biggest daily drop since 2014 (Recasts throughout, adds shares, analyst)
By Byron Kaye
Feb 12 (Reuters) - Australian electronics retailer JB Hi-Fi Ltd posted a record first-half net profit, but spooked investors by warning that earnings growth would slow amid fierce competition, knocking its shares down by more than 8 percent.
The muted outlook reflects the mounting concerns about the impact of e-commerce giant Amazon.com Inc's arrival in Australia in December. JB Hi-Fi and larger player Harvey Norman Holdings Ltd are among those expected to take an immediate hit from the entry of the online juggernaut.
JB Hi-Fi cautioned its annual profits would grow at a slower pace than its sales, indicating tighter margins, after earlier reporting a 21 percent jump in underlying net profit to A$151.7 million ($119 million) for the six months ended December.
Shares of the company fell as much as 8.5 percent after the news and were down 7.8 percent by 0122 GMT, on track for their biggest daily drop since 2014. The stock had climbed 17 percent since Amazon started in Australia on Dec. 5, amid criticism of a lacklustre opening from the U.S. giant.
"JB Hi-Fi has rallied strongly into this result on high expectations for Christmas trading (and) while this proved correct, concern is likely to build around gross margin pressure," Citi analysts wrote in a client note.
The company expects its full-year profit to grow 13-16 percent despite sales rising 22 percent.
Margins narrowed in the first half of the year too, with group sales up 41 percent, helped by demand for audio devices and drones, double the rate of its underlying net profit.
JB Hi-Fi added that sales from its appliances chain, The Good Guys, which it bought in 2016, grew just 1.8 percent on a comparable store basis in the six-month period.
For the month of January, The Good Guys sales fell 4.7 percent from the same month a year earlier, due to unusually strong air conditioner sales the previous January, it said.
Online sales for JB Hi-Fi rose 41 percent to A$119.3 million in the six-month period, a fraction of total sales which came in at A$2.48 billion.
JB Hi-Fi declared an interim dividend of 86 Australian cents per share, up from 72 Australian cents last year. ($1 = 1.2768 Australian dollars) (Reporting by Byron Kaye in SYDNEY Aaron Saldanha in Bengaluru; Editing by Himani Sarkar)