Update 1.20am: Turkish media reports cited MIT, the national intelligence agency, as saying the coup had been defeated. The MIT website was not immediately accessible from Turkey.
MIT spokesman Nuh Yilmaz said General Hulusi Akar, the military chief of staff, was back in control.
Mr Yilmaz said "General Akar is back on top of his duties. Everything is returning to normal."
Update 12.45pm: The Anadolu Agency has reported that a bomb has hit the Turkish parliament in Ankara.
Update 12.10am: Turkey's state-run Anadolu news agency has said 17 police officers were killed in a helicopter attack on police special forces headquarters in outskirts of Ankara.
Update 11.45pm: Turkish news agency Dogan said soldiers had opened fired on people trying to cross Istanbul's Bosporus bridge in protest of the attempted coup, and some had been wounded.
Turkey's Istanbul-based first army commander said the soldiers involved in the attempted coup "represent a small group" and "there is no cause for concern", according to the state-run Anadolu Agency.
Umit Dundar told Anadolu that "we are working to solve the problem here. They represent a small group within the First Army Command. There is no cause for concern. We are taking the necessary precautions with (soldiers) who have not joined them and remain within the military chain of command."
Soldiers on Bosphorus bridge in Istanbul shouting to communters: "Curfew has been imposed, go home!". https://t.co/XmIlEgHdrC— Has Avrat (@hasavrat) July 15, 2016
Update 11.20pm: Loud explosions were heard in Turkey's capital Ankara and CNN-Turk reported an explosion at the state-run television building.
Turkey's state-run news agency said military helicopters had also attacked the headquarters of TURKSAT satellite station on the outskirts of Ankara and the Ankara police headquarters.
Dozen of tanks were seen moving towards a palace that is now used by the prime minister and deputy prime ministers.
A civilian car tried to stop one of the tanks, but it rammed through the vehicle as those in the car escaped.
The White House said President Barack Obama hads been briefed on developments in the key Nato ally.
Flag-waving crowds gather in Istanbul's Taksim Square after Turkey's President urged people to take to the streets https://t.co/SxkRWtk7GF— SkyNews (@SkyNews) July 15, 2016
The National Security Council said Mr Obama had been apprised the "unfolding situation" in Turkey and would continue to get regular updates.
US secretary of state John Kerry says he hoped for stability and continuity in Turkey following the reports.
Mr Kerry, in Moscow for talks with Russian officials on Syria, said he did not have details of the situation rapidly unfolding on the ground in Turkey and said it would be "inappropriate" to comment on developments.
But he expressed hope that the key ally and strategically important member of the coalition fighting the Islamic State would remain at peace.
Update 11pm: Turkey's president has urged citizens to take to the streets in a show of support for the government after the military said it seized full control of the country.
Recep Tayyip Erdogan, speaking to CNN-Turk through FaceTime, called the actions by the military "an attempt at an uprising by a minority within our armed forces".
The president's office refused to disclose Mr Erdogan's whereabouts, saying he was at a secure location.
Mr Erdogan said "I don't believe this coup attempt will be successful.
"There is absolutely no chain of command here. Right now the chain of command has been put on hold."
Update 10.50pm: Reports of helicopters opening fire and a 'strong explosion' in Ankara.
#BREAKING Strong explosion heard in Turkish capital Ankara: AFP— AFP news agency (@AFP) July 15, 2016
Update 10.30pm: President Erdogan is calling on people of Turkey to go out into the streets, Reuters reported.
Update 10.25pm: Irish citizens in Turkey are advised to stay indoors until the situation becomes clearer.
The phone number for the Irish Embassy in Istanbul is +90 212 482 1862.
Update 10.20pm: A military statement read on state TV said armed forces have seized power, citing rising autocratic rule and increased terrorism.
Update 10pm: The Dogan agency reported that the statement said that the military did this "to reinstall the constitutional order, democracy, human rights and freedoms, to ensure that the rule of law once again reigns in the country, for the law and order to be reinstated".
The military statement went on to say that "all international agreements and commitments will remain. We pledge that good relations with all world countries will continue".
Update 9.50pm: Reports say the Turkish military has released a statement saying armed forces have "fully seized control" of running the country.
Update 9.45pm: AFP are reporting that Turkey's top general is being held hostage.
#BREAKING Turkey's top general 'held hostage' at military HQ: state agency— AFP news agency (@AFP) July 15, 2016
Update 9.40pm: "We are focusing on the possibility of an attempt (coup)," Mr Yildirim said.
"There was an illegal act by a group within the military that was acting out of the chain of military command. Our people should know that we will not allow any activity that would harm democracy."
The Dogan news agency says one-way traffic on the Bosphorus and Fatih Sultan Mehmet bridges were blocked. Video footage showed the bridge being blocked by military vehicles.
Turkish state-run television network TRT has been shut down, Bloomberg reported.
#BREAKING Turkey army says has taken power over country: TV— AFP news agency (@AFP) July 15, 2016
Earlier: A group within Turkey's military has engaged in what appeared to be an attempted coup, Turkey's prime minister says.
Binali Yildirim told NTV television: "It is correct that there was an attempt."
Mr Yildirim did not provide details, but said Turkey would never allow any "initiative that would interrupt democracy".
Earlier, military jets were heard flying over the capital, Ankara.
Media reports said ambulances were seen in front of Turkey's military headquarters.
Turkish soldiers block both bridges on the Bosphorus in Istanbul and jets flying low in Ankara. Reason not clear yet pic.twitter.com/tMG7KKYvGh— Selin Girit (@selingirit) July 15, 2016
A tank on the streets of Istanbul pic.twitter.com/9ZH9a769my— omar r quraishi (@omar_quraishi) July 15, 2016