A brick wall at a partly constructed church in Uganda's capital collapsed onto the congregation Wednesday during an evening thunderstorm, killing at least 27 people, authorities said.

At least 20 people were reported hospitalized. Police, firefighters and rescue personnel said they believed all the victims had been removed from the debris.

The Protestant evangelical church in a Kampala slum was under construction, and parishioners set up a wood-and-tin shack inside the unfinished structure so they could conduct services, regional police Commander Grace Puryagumanawe said.

"We're going to investigate the poor build standards. We have already collected samples of the materials used," he said.

Fire and rescue chief Joseph Mugisa said the wall collapsed during a thunderstorm with high winds and heavy rains, and 27 people were killed.

"It was completely chaotic," he said. "Everyone was trying to get out. People were yelling and shouting. People were trying to carry out the injured."

There is no electric power in the slum, and witnesses said rescuers burned plastic chairs to provide light for those digging through the rubble. After the chairs had all been burned, rescuers had to give up the search until dawn, witnesses said.