(Updates price, sectors) June 23 (Reuters) - Canada’s main stock index was flat on Wednesday as data showed domestic retail sales plunged in April and May, while energy stocks advanced on stronger crude prices. * The nation’s retail trade fell 5.7% in April, the sharpest decline in a year, as shops and other businesses were shuttered amid a third wave of COVID-19 infections, Statistics Canada data showed. * The energy sector climbed 1.4% as U.S. crude prices were up 1.6% a barrel, while Brent crude added 1.3%. * At 9:37 a.m. ET (13:37 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was up 3.54 points, or 0.02%, at 20,204.19. * The financials sector inched down 0.1% and the industrials sector fell 0.4%. * The materials sector, which includes precious and base metals miners and fertilizer companies, added 0.6% as gold futures rose 0.3% to $1,780.7 an ounce. * On the TSX, 115 issues were higher, while 111 issues declined for a 1.04-to-1 ratio favouring gainers, with 13.85 million shares traded. * The largest percentage gainers on the TSX were lithium miner Lithium Americas Corp, which jumped 3.7%, and miner Teck Resources Ltd, up 3.5%. * Empire Company Ltd fell 4.9%, the most on the TSX, after the conglomerate warned that it expects the pandemic to continue affecting the company during 2022, including its same-store sales. * The second-biggest decliner was uranium miner Nexgen Energy Ltd, down 3.6%. * The most heavily traded shares by volume were Power Corporation of Canada, TC Energy Corp and Surge Energy Inc. * The TSX posted 10 new 52-week highs and one new low. * Across all Canadian issues there were 48 new 52-week highs and eight new lows, with a total volume of 26.45 million shares. (Reporting by Amal S in Bengaluru; Editing by Devika Syamnath) Our Standards: The Thomson Reuters Trust Principles.