By Annie Gimbel |

HOUSTON (CBSDFW.COM) – Houston Mayor Sylvester Turner has imposed a midnight to 5 a.m. curfew.

There are just too many people in shelters, according to Turner and he doesn’t want them to have to worry about someone breaking into their home or looting.

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“Be very, very careful when people are knocking on your doors and impersonating law enforcement,” said Turner.

However, the curfew exempts flood relief volunteers, those seeking shelter, first responders and people going to and from work.

He said reports have come in about people dressed in khaki and black shirts going door-to-door telling people there’s a mandatory evacuation because the dam is about to give way.

The mayor reminded the community that unfortunately there are always people willing to take advantage of bad situations.

Federal and local agencies said they have rescued more than 13,000 people from Tropical Storm Harvey in Houston and surrounding areas.

Fifty members of the Texas National Guard are stationed at the George R. Brown Convention Center, which is now being used as a shelter. The Toyota Center is also being used as a shelter.