UPDATE 1-Rautaruukki posts Q1 loss, sees Q2 in the red

* Q1 operating loss 113 million euros, misses estimates

* Sees Q2 loss narrowing vs Q1

* Shares shed earlier gains

HELSINKI, April 23 (Reuters) - Finnish steel maker Rautaruukki (RTRKS.HE)reported on Thursday a deeper-than-expected first-quarter loss due to meagre demand, and said losses would continue until end-June at least.

The firm reported a January-March operating loss of 113 million euros ($147.2 million), down from a profit of 143 million a year ago and missing all estimates in a Reuters poll where the average expectation was for a loss of 40 million.

Net sales plunged 46 percent to 506 million euros, well below expectations in the poll of 642 million and at the low end of the range.

"Demand for steel products fell sharply in all customer industries and markets," Rautaruukki said in a statement.

The firm said that it expected second-quarter sales to be on a level similar to the first, with its loss to narrow.

"The company considers it has the potential to achieve a positive result before taxes during the second half of the year," it said, citing its ongoing restructuring programme.

Rautaruukki said in a separate statement it would spend 280 million euros to upgrade its Raahe mill in Finland.

Rautaruukki shares, trading higher ahead of the result, shed some gains to trade up 0.35 percent at 14.50 euros at 0941 GMT. ($1=.7678 euros)