Australian officials in Egypt are providing consular assistance to an award-winning Australian journalist arrested on suspicion of illegally broadcasting news harming "domestic security".
The arrests come amid a widening crackdown on the Muslim Brotherhood of ousted president Mohamed Morsi, which the military-installed government declared a "terrorist organisation" last week.
Al-Jazeera confirmed the arrests, and said police also detained a producer and a cameraman.
The Department of Foreign Affairs and Trade said on Monday night that it was "aware of reports on this matter".
"Australian officials in Cairo are providing consular assistance," a DFAT spokesman said in a brief statement.
Officers of the National Security service raided the broadcaster's makeshift bureau at a Cairo hotel on Sunday, arresting two of the journalists and confiscating their equipment, said a ministry statement.
It did not identify the journalists, only saying one was a "Muslim Brotherhood member" and the other an Australian.
Al-Jazeera English identified them as Cairo bureau chief Mohamed Adel Fahmy, a dual Egyptian-Canadian citizen, and Australian reporter Peter Greste.
It said producer Baher Mohamed and cameraman Mohamed Fawzi were also arrested on Sunday evening.
The raid came after authorities listed the Brotherhood as a terror outfit, making membership in the Islamist group or even possession of its literature a crime.
The journalists "broadcast live news harming domestic security", the ministry said, adding they were also found in possession of Brotherhood "publications".
Greste, a former BBC journalist, won the prestigious Peabody award in 2011 for a documentary on Somalia. Fahmy, who formerly worked with CNN, is a well-known journalist in Cairo with no known links to the Brotherhood.
"We condemn the arbitrary arrest of Al-Jazeera English journalists working in Cairo and demand their immediate and unconditional release," the network said.
"Al-Jazeera Media Network has been subject to harassment by Egyptian security forces which has arrested our colleagues, confiscated our equipment and raided our offices despite that we are not officially banned from working there."
Egypt's military-installed government cracked down on Al-Jazeera's affiliates following the overthrow of Morsi in July, accusing the broadcaster of pro-Brotherhood coverage.
Gas-rich Qatar had been a strong supporter of Morsi, and stood out among other Gulf nations in condemning Egypt's deadly crackdown on pro-Morsi demonstrations.
Several Al-Jazeera reporters remain in detention, including Abdullah Elshamy, a journalist for the Arabic language station arrested on August 14 when police dispersed an Islamist protest camp in Cairo, killing hundreds in clashes.
The government declared the Brotherhood a "terrorist organisation" last week after a suicide car bombing of a police headquarters killed 15 people.
It blamed the attack on the Islamists, although an al-Qaeda-inspired group claimed responsibility for the bombing and the Brotherhood condemned it.
Media watchdog the Committee to Protect Journalists said in a report that Egypt came third for the number of journalists killed on the job in 2013, after Syria and Iraq.
