Officials on Thursday said at least four people were killed in Texas as heavy storms with winds up to 160 kilometres per hour lashed the US state.

Streets in downtown Houston were covered in glass from blown-out windows, video and photos posted to social media showed, as the National Weather Service warned of "severe" thunderstorms and possible tornadoes.

Downed trees and power lines littered residential areas, and around a million customers in the state had lost power -- including more than 800,000 in Harris County, where Houston is located.

The mayor of Houston, John Whitmire, urged residents to avoid downtown, adding that public schools would be closed on Friday and asked non-essential workers to stay home as well.

The mayor and the city's office of emergency management (OEM) were working with first responders to assess the damage, the city said.

Residents were asked to stay off the roads and avoid unnecessary travel, according to the OEM. (AFP)