Police disrupted a terrorist plot to bring down an airplane and arrested four men on Saturday in raids on homes in several Sydney suburbs, the prime minister said.

Prime Minister Malcolm Turnbull said on Sunday that security had been increased at Sydney Airport since Thursday because of the plot. The increased security measures had been extended to all major international and domestic terminals around Australia overnight.

"I can report last night that there has been a major joint counterterrorism operation to disrupt a terrorist plot to bring down an airplane," Turnbull told reporters. "The operation is continuing."

Australian Federal Police Commissioner Andrew Colvin said details were scant on the specifics of the attack, the location and timing.