From this:

President Bush has signed a directive granting extraordinary powers to the office of the president in the event of a declared national emergency, apparently without congressional approval or oversight.

The "National Security and Homeland Security Presidential Directive" [whitehouse.gov/news/releases/2007/05/20070509-12.html]was signed May 9, notes Jerome R. Corsi in a WND column.

...The directive establishes under the office of the president a new national continuity coordinator whose job is to make plans for "National Essential Functions" of all federal, state, local, territorial and tribal governments, as well as private sector organizations to continue functioning under the president's directives in the event of a national emergency.

It's a National Security Presidential Directive (NSPD-51) and a Homeland Security Presidential Directive (HSPD-20) and it creates a national continuity coordinator who would be Frances Townsend.

"Catastrophic emergency" is loosely defined as "any incident, regardless of location, that results in extraordinary levels of mass casualties, damage, or disruption severely affecting the U.S. population, infrastructure, environment, economy, or government functions."

Corsi says the president can assume the power to direct any and all government and business activities until the emergency is declared over...

The directive also makes no reference to Congress and its language appears to negate any requirement that the president submit to Congress a determination that a national emergency exists...

Much more at both links, and in case you think this would only be for continuity of government, note that it apparently supercedes the more Constitutionally-correct National Emergency Act, which explicitly involves Congress. Also note this May 2005 story:

The Bush administration periodically put the USA on high alert for terrorist attacks even though then-Homeland Security chief Tom Ridge argued there was only flimsy evidence to justify raising the threat level, Ridge now says.