Discount store operator Dollar Tree Inc (DLTR.O) reported lower-than-expected holiday quarter same-store sales on Wednesday, sending its shares down as much as 13 per cent in premarket trade.

Same-store sales at Family Dollar, the unit it acquired three years ago, rose one per cent. Same-store sales at Dollar Tree rose 3.8 per cent.

Wall Street analysts had expected Family Dollar to report same-store sales growth of 1.46 per cent and 3.99 per cent for its core Dollar Tree stores, according to Thomson Reuters I/B/E/S.

Overall, sales at established stores rose 2.4 per cent, lower than the average analyst estimate of 2.73 per cent.

Net income rose to US$1.04 billion, or US$4.37 per share, in the fourth quarter ended Feb. 3, from US$321.8 million, or US$1.36 per share, a year earlier.

Excluding items, Dollar Tree earned US$1.89 per share, missing analysts' average estimate by a cent.

The company recorded a tax benefit of US$583.7 million in the latest quarter due to changes in the U.S. tax code.

Net sales rose to US$6.36 billion from US$5.64 billion.