Militants launched a suicide attack on Kabul shortly after dawn on Monday, police said, with loud explosions and gunfire heard near the Afghan capital's airport.

Several blasts and bursts of small-arms fire erupted for at least 45 minutes and were ongoing, with the US embassy sounding its "duck and cover" alarm and its loudspeakers warning that the alarm was not a drill.

"It's an ongoing gunfight and blasts, and I can tell you that it's a suicide group attack," Hashmat Stanikzai, Kabul's police chief, told AFP.

Stanikzai said he was unable to confirm the target of the attack, but the explosions came from close to the airport area on the northeast side of the city.