AMSTERDAM - Shares in Vopak, the Dutch oil and chemicals storage company, tumbled on Friday after it said it did not expect Asian markets to improve and that its core earnings were likely to be lower in the second half of the year. Vopak said its first-half earnings rose 17 percent thanks to good trading conditions in North America and Europe, offset by the impact of China’s economic slowdown. But investors dumped the stock on the company’s worsening outlook, sending the stock down more than 15 percent, poised for its worst trading day in nearly three decades. The results coincided with data showing the Chinese factory sector shrank at its fastest rate in almost 6-1/2 years. . Vopak, the world’s largest independent storage tank operator, reiterated its April forecast for full year EBITDA, or earnings before interest, taxes, depreciation and amortisation, in excess of 763 million euros ($858 million) for 2015. However, that implies a decline in the second half of the year after the company reported EBITDA of 408 million euros in the first half of 2015. Vopak Chief Executive Eelco Hoekstra confirmed a decline in the second half was the most likely scenario. “If you do not expect or see signals for significant improvements for the Asian results in the second half of the year…then it’s more likely of course that the second half of the year is lower than the first half,” he said. To meet current guidance, the company would have to report EBITDA of at least 355 million in the second half—which would represent a 13 percent fall from first half levels. Vopak said the impact of divestments would also be felt in the second half of the year. The company is in the process of divesting 15 primarily smaller terminals, which contributed around 4 percent to 2014 earnings, to focus on markets with higher demand, largely in the Middle East and Asia. ($1 = 0.8895 euros)