A vehicle burns after an explosion in Ankara, Turkey, March 13, 2016. [Photo/Agencies]

ANKARA - A car bomb tore through a crowded transport hub in the Turkish capital, Ankara, on Sunday, killing at least 34 people and wounding 125 in the second such attack in the administrative heart of the city in under a month.

The blast, which could be heard several kilometres away, sent burning debris showering down over an area a few hundred metres (yards) from the Justice and Interior Ministries, a top courthouse, and the former office of the prime minister.

"These attacks, which threaten our country's integrity and our nation's unity and solidarity, do not weaken our resolve in fighting terrorism but bolster our determination," President Tayyip Erdogan said in a statement.

There was no immediate claim of responsibility, but Interior Minister Efkan Ala said the name of the group behind the attack would likely be announced on Monday after initial investigations were completed.

"Tonight, civilian citizens waiting at a bus stop were targeted in a terrorist attack with a bomb-laden car," Ala told reporters after a meeting with Prime Minister Ahmet Davutoglu, the head of the intelligence agency and security chiefs.

"Significant findings have been made, but the organisation behind this will be announced once the investigation has been finalised," he said.

NATO member Turkey faces multiple security threats. As part of a US-led coalition, it is fighting Islamic State in neighbouring Syria and Iraq. It is also battling PKK militants in its southeast, where a 2-1/2-year ceasefire collapsed last July, triggering the worst violence since the 1990s.

The United States condemned the attack, saying in a White House National Security Council statement: "This horrific act is only the most recent of many terrorist attacks perpetrated against the Turkish people. The United States stands together with Turkey, a NATO ally and valued partner, as we confront the scourge of terrorism."

Health Minister Mehmet Muezzinoglu said 30 of those killed had died at the scene, while the four others died in hospital. At least one or two of the dead were attackers, he said, and 19 of the 125 wounded were in critical condition.