He said he had signed a decree that would increase the government's powers for 15 days, as set forth in Chad's constitution.
Deby said the decree instituted "measures important and urgent to maintain order, guarantee stability and assure the good functioning of the state".
The text of the decree, which was read out on the broadcast, announces that, as of Friday, there is "a state of emergency throughout the territory of the Republic of Chad".
The measure gives extra powers to regional governors to control the circulation of people and vehicles, bans most meetings, allows the government to control what is published in the press, and institutes a midnight-to-6am curfew.
After the 15-day period, the country's national assembly decides whether to allow an extension of the state of emergency.
The declaration followed the attack at the beginning of February on the capital, Ndjamena, by forces from eastern Chad seeking to overthrow the government.
After a weekend of fighting in which clashes reached the edge of the presidential palace, Chad's army repelled the fighters who moved eastward towards the Sudanese border.