"We have decided to declare a state of emergency to ensure that our (rescue and recovery) work can be carried out quickly," Erdogan said in televised remarks.
"We will quickly complete the presidential and parliamentary processes related to this decision, which will cover our 10 provinces where the earthquake has been experienced and will last for three months."
Erdogan's government is coming under growing pressure on social media for what his critics view as a slow response to Turkey's biggest earthquake in nearly a century.
The latest toll showed Monday's 7.8-magnitude tremor and its aftershocks killing 3,549 people in Turkey and 1,602 in government- and rebel-controlled parts of Syria.
Erdogan said his government would send more than 50,000 aid workers to the area and allocate 100 billion liras ($5.3 billion) in financial help.
Erdogan's handling of the biggest natural disaster in his two-decade rule could prove crucial ahead of tightly-contested parliamentary and presidential polls on 14 May.