Manufacturing activity in the New York region improved significantly in May, according to a survey released Thursday by the Federal Reserve Bank of New York. According to the latest Empire State Manufacturing Survey, the general business conditions index jumped 18 points to 19, its highest level in nearly four years. The new orders and shipments indices also posted sharp gains, rising to 10.4 and 17.4, respectively. Employment expanded significantly, although the average workweek index held steady at 2.2. The index for the number of employees rose 13 points to 20.9. Moreover, indices for the six-month outlook were highly optimistic. The index for future general business conditions rose six points to 44, its highest level in more than two years, with 53 percent of respondents expecting conditions to improve over the next six months. The Empire State manufacturing index closely watches manufacturing activity in New York, northern New Jersey and southern Connecticut. The Federal Reserve Bank of New York conducts the survey monthly and participants represent a variety of industries.