* Shares fall as much as 6.3 pct
* Nucor expects 2nd-qtr earnings of $1-$1.05/shr
* Warns of weakness in steel mills unit (Compares profit with analyst estimates; updates shares)
June 15 (Reuters) - U.S. steelmaker Nucor Corp on Thursday forecast second-quarter earnings per share below estimates, hurt in part, by weak demand in its steel mills business.
Nucor's shares fell as much as 6.3 percent to $55.40 in morning trading after the company said it expects earnings of $1.00 to $1.05 per share for the second quarter ending July 1. Analysts on average were expecting $1.22 per share, according to Thomson Reuters I/B/E/S.
Shares of other U.S. steelmakers including U.S. Steel Corp , AK Steel Holding Corp and Steel Dynamics Inc , fell 3 to 5 percent.
"Market conditions for hot-rolled sheet products have been more challenging than we expected earlier in the quarter when we provided our qualitative guidance due to aggressive competition," Nucor said in a statement.
Imports continued to hurt the U.S. steel industry, the company added.
China, the world's largest steel producer, makes far more steel than it consumes, selling the excess output overseas in markets such as the United States, often undercutting domestic producers.
Last week, American steel executives said a Trump administration national security review of their industry could provide relief from imports that dozens of U.S. Commerce Department anti-dumping cases have only partly offered.
Steel stocks have received a boost from Donald Trump's election as president, with optimism that his administration will promote the domestic industry.
The S&P 1500 steel sector index had climbed 9.8 percent since Trump's election, while Nucor's shares had risen 15 percent. (Reporting by Arunima Banerjee in Bengaluru; Editing by Sai Sachin Ravikumar)