MANAMA, Bahrain  Without warning, hundreds of heavily armed riot police officers rushed into Pearl Square here early Thursday, firing tear gas and concussion grenades at the thousands of demonstrators who were sleeping there as part of a widening protest against the nation’s absolute monarchy.

Men, women and young children ran screaming, choking and collapsing.

The square was filled with the crack of tear gas canisters and the wail of ambulances rushing people to the hospital. Teams of plainclothes police officers carrying shotguns swarmed through the area, but it was unclear if they used the weapons to subdue the crowd.

“There was a fog of war,” said Mohammed Ibrahim as he took refuge in a nearby gas station. He was barefoot, had lost his wallet and had marks on his leg where he said he had been beaten. “There were children, forgive them.”

At least two people were killed in the mayhem, according to witnesses at a nearby hospital and news agency reports. Many people were injured in the chaos  trampled, beaten or suffocated by the tear gas.