* Indexes down: Dow 0.8 pct, S&P 0.7 pct, Nasdaq 0.7 pct
By Ryan Vlastelica
NEW YORK, Sept 29 (Reuters) - U.S. stocks were sharply lower on Monday, extending the previous week's decline on heavy volume as investors monitored the continued civil unrest in Hong Kong for any potential impact on Chinese growth.
The day's losses were broad, with nine of the ten primary S&P 500 sectors lower on the day. The only group to rise, utilities, are viewed as a defensive play and were up less than 0.1 percent. Energy stocks were the biggest losers, off 1.1 percent.
The S&P 500 fell back below its 50-day moving average, a sign of weak near-term momentum. Last week, major indexes suffered their biggest weekly decline of the past eight.
Volume was heavier than average, and market participants said more traders were in the office following a period where many were out for vacation.
"People are finally back from vacation, and school is back in session, so we're finally seeing some volume, with a lot of traders catching up and picking a direction after last week's wrestling match," said Frank Davis, director of sales and trading at LEK Securities in New York.
"Everyone is talking about the Hong Kong overhang. That's definitely the kind of thing that will go into your short-term view."
China faced one of its biggest political challenges since the Tiananmen Square massacre as hundreds of democracy protesters faced down tear gas and police baton charges. Though the economic fallout from the unrest was uncertain, Chinese growth has been a major driver of global share gains in recent years, although recent data has pointed to slowing conditions. An extended period of unrest could raise further questions about the economy's prospects.
The Dow Jones industrial average was falling 138.39 points, or 0.81 percent, to 16,974.76, the S&P 500 was losing 14.38 points, or 0.73 percent, to 1,968.47 and the Nasdaq Composite was dropping 29.99 points, or 0.66 percent, to 4,482.20. At current levels, the S&P is about 2.1 percent away from a record close hit earlier this month.
Declining issues were outnumbering advancing ones on the NYSE by 2,390 to 392, for a 6.10-to-1 ratio on the downside; on the Nasdaq, 1,836 issues were falling and 490 advancing for a 3.75-to-1 ratio favoring decliners.
The benchmark S&P 500 index was posting 1 new 52-week high and 9 new lows; the Nasdaq Composite was recording 12 new highs and 72 new lows. (Editing by Nick Zieminski)