Houston has imposed an overnight curfew beginning at midnight Tuesday for an indefinite period amid incidents of looting, armed robberies and people impersonating police officers, city officials said.

The curfew will run from midnight until 5 pm It originally was due to begin at 10 pm but the city pushed the start back two hours to allow volunteers to continue working, Mayor Sylvester Turner said in a statement. The city is also bringing additional police from other regions.

‘You cannot drive, nor be in any public place. We have had problems with armed robberies, with people with guns and firearms,’ said Houston Police Chief Art Acevedo.

Turner earlier said the city was opening several additional emergency shelters to alleviate crowding at the convention center, which has 10,000 people. Some of those will be moved to a nearby concert hall and basketball arena.

One shelter will open on the city’s west side, near where more than 3,000 homes have been flooded. Another center in Humble, Texas, will house people from the city’s northern suburbs, the mayor added.