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QUITO, Ecuador (AP) _ A grenade accidentally detonated in the ammunition depot of an Ecuadorean army base, setting off 20 minutes of explosions that killed six people, injured at least 200 others and caused chaos in the surrounding city.

Fire and shock waves from Wednesday's blasts in the Galapagos Mechanized Army Base spilled into Riobamba, a sedate Andean city of 100,000, blowing out windows a mile away.

``It was like an earthquake, windows blew out and the panic was irrepressible,'' Riobamba Mayor Fernando Guerrero said.

Riobamba, 100 miles south of the capital, Quito, is home to most of Ecuador's tank units and about 1,500 soldiers.

The blast cut telephone and power lines. By nightfall rescuers were left in the dark to seek out survivors. People living near the base were evacuated.

Army spokesman Col. Arturo Cadena told local television that the first explosion was caused by a hand grenade and that five people _ three civilians and two soldiers _ were killed in the blasts.

Later, the Red Cross issued a statement saying six people, including two soldiers, had been killed and 200 people others injured, most of them from glass shards.

The Red Cross said the number of victims inside the base was not known because rescue teams were being held back by the danger that more munitions might explode. The statement also said that buildings in the surrounding blocks had received considerable damage from the blasts.

Military patrols cruised the city for hours after the explosions began and as the city sank into darkness, asking people living near the base to evacuate the city, El Comercio, Quito's leading paper, reported Thursday from Riobamba.

Hundreds of people wandered the streets, screaming each time a thunderous roar ripped from the base. Many were looking for missing relatives.

Many people who lived near the base refused to evacuate until they learned what had happened to their loved ones, the paper reported.

``I thought it was an eruption of Tungurahua volcano and suddenly the doors and the windows blew out,'' said Jorge Nager, a retired military man who lives just across the street from the base.

``A piece of glass 30 centimeters (one foot) long fell on the main avenue,'' Nager said.

The streets for blocks around the base were covered with broken glass and metal fragments, El Comercio reported.

Many of the people who were taken to hospitals for treatment had received cuts from flying glass and many of them were children, the paper said.

At the Riobamba Policlinico, one of the city's main hospitals, there were scenes of chaos as the injured were brought in. Hundreds of people arrived looking for injured relatives.

The waiting room was converted into an emergency room. To one side on a cot a young soldier was awaiting treatment for second degree burns over most of his body. He had difficulty talking but he told the paper that although he was far from the ammunition depot, the explosion threw him high into the air.

The explosion came four days before a Nov. 24 runoff election for president. Former coup leader Lucio Gutierrez has led millionaire businessman Alvaro Noboa in recent polls. The winner will replace President Gustavo Noboa, who took office following a 2000 coup spearheaded by Gutierrez.