A state of emergency is an official declaration by a government in which it asserts extraordinary powers to govern in the face of some crisis. It gives the government sweeping powers to change laws and suspend normal civil liberties in the area where it is declared. It is often used to deal with natural disasters, civil unrest, a medical pandemic or epidemic, armed conflict, a terrorist threat or other biosecurity risk.
The President has a range of executive powers that it can invoke during a state of emergency, including suspending civil rights like the right to free speech and assembly, and allowing searches without a warrant. Those restrictions are normally only permitted to the extent they are necessary to deal with the situation that is being dealt with.
Congress can impose additional limitations on the power of the president during a state of emergency, and it can limit the duration of a state of emergency. In the United States, a state of emergency can be renewed for one year with approval from Congress. The Governor of a state can also issue an emergency declaration that grants more expansive powers to their executive branch.
In the United Kingdom, the Sovereign on the advice of the Privy Council or a Minister of the Crown can introduce emergency regulations (often called “state of war”) to deal with an act of terrorism that threatens serious damage to the UK or other events that present a grave national security threat. These emergency measures can also extend to certain private sectors and entail suspending civil liberties such as freedom of movement, secrecy of correspondence or the right to protest.