UPDATE 3-Oil protesters cause partial shutdown of Houston Ship Channel in Texas

(Adds byline, dateline, protest coincides with presidential debate, Exxon plant operations continue)

By Erwin Seba

HOUSTON, Sept 12 (Reuters) - The U.S. Coast Guard on Thursday closed part of the Houston Ship Channel to vessel traffic near Baytown, Texas, after 11 Greenpeace USA protesters suspended themselves by cables over the key oil export waterway.

The closure of one portion of the channel, which stretches 53 miles (85 km) from its entrance in the Gulf of Mexico to the Port of Houston, blocked tanker ship traffic to and from five major oil refineries as well as chemical and oil-export terminals.

In Twitter messages posted by Greenpeace USA, protesters can be seen dangling on harnesses from the bridge over the waterway, with large yellow banners flapping in the wind.

"We're in the heart of the fossil fuel industry (the largest oil export channel in the U.S.) to confront Trump & the oil industry," one tweet said. "It is time to end the age of oil," said another.

The protest came hours ahead of a planned debate in Houston by 10 Democratic White House contenders that has drawn national media to the fourth-largest U.S. city.

Just one ship was waiting to enter the busiest U.S. petrochemical port, and two ships were waiting to exit the waterway, the Coast Guard said.

The area affected by the closing is near Exxon Mobil Corp's 560,500-barrel-per-day refinery in Baytown, which is 26 miles (42 km) east of Houston.

Production at the refinery was unaffected by the channel closure, people familiar with the matter told Reuters. The Baytown refinery is the fourth-largest in the United States and Exxon's largest in the country.

Other refiners along the channel affected by the shutdown included Valero Energy Corp's 205,000-bpd Houston refinery, LyondellBasell's 263,776-bpd Houston refinery, Chevron Corp's 112,229-bpd Pasadena, Texas, refinery and Royal Dutch Shell Plc's 340,000-bpd Deer Park, Texas, refinery.

All of the refineries are able to ship out products via pipelines and most have enough crude on hand to continue operating at maximum capacity for several days.

The channel was closed from Light 102A to Light 104, the Coast Guard said in a notice. Ship traffic to Texas City, Texas, where two refineries and several chemical plants are located, was not affected by the closure on the upper Ship Channel. (Reporting by Erwin Seba in Houston and Swati Verma in Bengaluru ; Editing by Bernadette Baum)