BAXTER, Tenn. (AP) — A grim search continued Wednesday for survivors of deadly tornadoes in Tennessee, where 24 people were killed and 21 others remain missing.

Gov. Bill Lee declared an emergency and sent the National Guard to help with search-and-rescue efforts.

The twisters struck after midnight Tuesday, tearing apart more than 140 buildings and burying some people in the rubble as they slept.

People across Nashville were awakened by outdoor sirens alerting them to the tornado danger, but these warning systems don't exist in some rural areas.

Some survivors credit the alerts that blared from their cellphones for saving their lives.

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