(Reuters) - Shares of Carvana ( CVNA ) surged more than 30% in extended trading on Wednesday after the used-car seller forecast a surprise rise in current quarter retail sales and core profit. Carvana's ( CVNA ) results come as high interest rates prompt consumers to look for deals on second-hand cars instead of buying new ones.

Its shares, which have a short interest of 27% of free float, are up about 65% this year after recording a 11-fold rise last year.

The stock surge is set to add about $6 billion to its market capitalization of $17.6 billion, as of Wednesday's close.

The used-car retailer said it was expecting a sequential increase in adjusted core profit and growth rate in retail units in the second quarter, while analysts expected a 2.6% fall in retail sales from a year earlier.

The total supply of unsold used vehicles on dealer lots across the United States rose 9%, to 2.27 million units in March from a year earlier, according to Cox Automotive.

The company reported a first-quarter profit of $49 million, compared with analysts' estimates of $31.2 million, according to LSEG data.

It said adjusted earnings before interest, tax, depreciation and amortization in the first quarter were $235 million, exceeding capital expenditures and interest expense. Analysts had expected $135.9 million in adjusted core earnings.

(Reporting by Akash Sriram in Bengaluru; Editing by Anil D'Silva)