At least 28 people have been killed and dozens injured after an explosion hit the Turkish capital of Ankara.

Police said a car bomb was detonated near a military headquarters, sending dark smoke billowing into the sky, at around 6.30pm.

The Turkish military said that several buses carrying military personnel were deliberately attacked as they waited at traffic lights.

The rush-hour blast was 300m in front of the Chief of Staff's Building, the base for the heads of Turkey's Army, Air Force and Navy and close to the seat of parliament.

At least two or three buses and several cars are believed to have been set on fire. Dozens of emergency vehicles were sent to the scene.

A spokesman for the Turkish government said that 28 were killed and 61 were injured, revising earlier figures.

A Turkish security official told Reuters that early signs indicated that the Kurdistan Workers Party (PKK) was behind the attack but the government spokesman said it was too early to say.

Other security sources in the southeast, however, said they believed Islamic State militants may have been behind the bombing.

There was no immediate claim of responsibility.

The blast forced Turkish Prime Minister Ahmet Davutoglu to postpone a trip to Brussels where he was due to discuss the migrant crisis with EU leaders, his office said. 

The EU later said that the planned conference on refugees had been cancelled as a result.

A blackout on the reporting of the explosion by local media was imposed - something Turkey has done during similar events in the past.