Turkish Prime Minister Binali Yildirim said 36 were dead and Justice Minister Bekir Bozdag said 147 were wounded. Another senior government official told The Associated Press the death toll could climb much higher.

The senior official, who spoke on condition of anonymity in line with government protocol, at first said close to 50 people had already died, but later said that the figure was expected to rise to close to 50.

Yildirim said three suicide bombers were responsible for the attack and all initial indications suggest the Islamic State group was behind it.

He said the attackers arrived at the airport in a taxi and blew themselves up after opening fire. Asked whether a fourth attacker might have escaped, he said authorities have no such assessment but are considering every possibility.

The victims included some foreigners, he said, adding that many of the wounded have minor injuries but others are more badly hurt.

Another Turkish official said two of the attackers detonated explosives at the entrance of the international arrivals terminal after police fired at them, while the third blew himself up in the parking lot.

The official, who also spoke on condition of anonymity in line with government protocol and cited interior ministry information, said none of the attackers managed to get past security checks at the terminal's entrance.

Turkish airports have security checks at both the entrance of terminal buildings and then later before entry to departure gates.

Roads around the airport were sealed off for regular traffic after the attack and several ambulances could be seen driving back and forth. Hundreds of passengers were flooding out of the airport and others were sitting on the grass.

Hevin Zini, 12, had just arrived from Duesseldorf, Germany, with her family and was in tears from the shock.

"There was blood on the ground," she told The Associated Press. "Everything was blown up to bits... if we had arrived two minutes earlier, it could have been us."

South African Judy Favish, who spent two days in Istanbul as a layover on her way home from Dublin, had just checked in when she heard an explosion followed by gunfire and a loud bang.

She says she hid under the counter for some time.

Favish says passengers were ushered to a cafeteria at the basement level where they were kept for more than an hour before being allowed outside.

Two South African tourists, Paul and Susie Roos from Cape Town, were at the airport and due to fly home at the time of the explosions.

"We came up from the arrivals to the departures, up the escalator when we heard these shots going off," Paul Roos said. "There was this guy going roaming around, he was dressed in black and he had a hand gun."

The private DHA news agency said the wounded, among them police officers, were being transferred to Bakirkoy State Hospital.

Turkey has suffered several bombings in recent months linked to Kurdish or Islamic State group militants.

The bombings include two in Istanbul targeting tourists that authorities have blamed on the Islamic State group.

The attacks have increased in scale and frequency, scaring off tourists and hurting the economy, which relies heavily on tourism revenues.

Istanbul's Ataturk airport was the 11th busiest airport in the world last year, with 61.8 million passengers, according to Airports Council International. It is also one of the fastest-growing airports in the world, seeing 9.2 percent more passengers last year than in 2014.

The largest carrier at the airport is Turkish Airlines, which operates a major hub there. Low-cost Turkish carrier Onur Air is the second-largest airline there.