(JTA) — Jewish communities in Australia remained under lockdown as a hostage crisis continued at a café in Sydney.

The Community Security Group, which handles security for the Jewish communities of Australia, raised the threat level to severe on Monday after an apparent Islamist gunman entered a café in downtown Sydney and took dozens of hostages,  the Australian Jewish News reported.

The Australian Jewish News reported that Jewish day schools throughout the country tightened security measures on Monday and cancelled all planned excursions.

The heightened alert will remain in effect on Tuesday, on orders from the Community Security Group, according to the newspaper.

The armed hostage-taker ordered his hostages to hold up a black flag with Islamic symbols and Arabic writing in the window of the Lindt Chocolate shop. Police reportedly made contact with the gunman on Monday night in Sydney. Five hostages have escaped and at least 30 remain.

Israel’s Defense Minister Moshe Yaalon said Monday in an interview on Israel Radio that Israel has been in contact with Australian officials and has offered its assistance in dealing with the crisis.

A popular religious Israeli singer, Benny Elbaz, and his son, Gad, left the café moments before it came under siege, which the singer called his “Hanukkah miracle” in media interviews. Elbaz is currently on tour in Australia.