Tanks opened fire around the Turkish parliament building and military jets were seen flying low over the city as the Turkish military claimed it has seized control of the country late on Friday night.
Turkish President Tayyip Erdogan, addressing Turkey via Facetime, asserted he is President and vowed to crush the opposition forces.
“I am calling on our nation. Go to squares, let us give them the best answer,” Erdogan said in a video message, “I do not believe this coup attempt will be successful. No coup-plotter in history has ever succeeded,” he said.
First Army commander Umit Dundar said that the coup-plotters represent a small minority in First Army command. “There is nothing to worry about. We are taking necessary measures with the soldiers who have not joined them and are still acting within chain of command.”
Erdogan said he was Turkey's commander in chief and there had not been any attempt against him. The Turkish presidency said the president is at a secure location.
Erdogan identified the group as belonging to the FETO/PDY terrorist organization, which three years ago staged an unsuccessful overthrow of the government, Turkey's Anadolu agency reported.
“This is an insurgency against democracy and national will,” Prime Minister Binali Yildirim told the nation on live TV late on Friday night. “We will not allow it. There will never be any compromise on democracy. The perpetrators will pay the heaviest price.”
State broadcaster TRT said the military had declared martial law and a curfew, in a statement signed by a group calling itself the "Council for Peace in the Homeland".
"The power in the country has been seized in its entirety," said a military statement quoted by Turkish media.
It said the coup had been launched "to ensure and restore constitutional order, democracy, human rights and freedoms and let the supremacy law in the country prevail, to restore order which was disrupted".
"All our international agreements and commitments retain their validity," the statement added.
"We hope our good relations will continue with all countries in the world."
The presidency said the statement was invalid.
Major bridges, Bosphorus Bridge and Fatih Sultan Mehmet Bridge, in Istanbul were closed and gunfire was heard at Istanbul airport as soldiers took to the streets of Ankara and Istanbul.
There were reports that coup attempters opened fire on civilians, who hit the streets in several cities to protest the attempt, Hurriyet Daily News online reported.
Soldiers fired bullets at civilians who walked to the Bosphorus Bridge.
Another incident was in the Bayrampasa district of Istanbul, where one person was wounded.
Prime Minister Binali Yildirim said those responsible for what he described as an attempted coup by a faction within the military would pay the highest price.
He said they would not be allowed to do anything to interrupt democracy.
Meanwhile, President Erdogan is reportedly seeking asylum in Europe, amid the military coup.
US military sources were quoted as telling NBC News that Erdogan's presidential jet was allegedly denied landing rights at Istanbul's airport, before it headed out of the country.
He was then denied asylum in Germany, according to NBC, before heading to London.
He also said "This country can't be managed from Pennsylvania," directly linking the coup attempt to US-based exiled imam Fethullah Gulen.