(Adds details and background)

RABAT, Sept 30 (Reuters) - Morocco's economic growth slumped to 0.5 percent year-on-year in the second quarter of 2016 from 4.2 percent in the same period last year after a severe drought hit the agricultural sector, its planning authority (HCP) said on Friday.

Agricultural output declined by 10.9 percent, it said in a statement. The agency reported in July that it expected Moroccan gross domestic product growth to slow to 1.2 percent in the third quarter of 2016.

In May, the Agriculture Ministry reported that the cereal crop in 2016 had fallen to 3.35 million tonnes, down 70 percent from last season's record 11 million tonnes, due to the worst drought to affect the North African kingdom in 30 years. Agriculture accounts for more than 15 percent of the economy.

After GDP growth of nearly 5 percent in 2015, the finance ministry expects it to ease to under 2 percent in 2016. The central bank has said GDP growth would stand at 1.4 percent this year.

Growth for the $100 billion economy in the first quarter of 2016 stood at 1.7 percent, according to charts included in the planning authority's statement.

(Reporting by Aziz El Yaakoubi) ((aziz.elyaakoubi@thomsonreuters.com; +212623934595)(;))