The Gulf state blew past a Sunday deadline to meet a series of demand that from Saudi Arabia and its allies that Doha describes as an "affront to international law."
If Qatar wants to end a recent diplomatic standoff, Saudi Arabia and three other Arab states say the country has 10 days to comply with a steep list of demands, including shutting down Al-Jazeera.
Erdogan says the state of emergency will make it easier to question and try the thousands of people accused of backing the failed coup attempt over the weekend, NPR's Peter Kenyon reports.
Al-Jazeera America, the news network that was backed by the ruling family of Qatar and struggled to gain traction in the U.S., will sign off for good after a three-hour farewell broadcast on Tuesday.
Australian Peter Greste, who spent more than a year in an Egyptian prison, was freed on Sunday. He says he remains concerned about his still-jailed Al-Jazeera colleagues.