Australians have been warned not to travel to southern Beirut in the wake of a car bombing that killed at least 20 people and injured more than 250.

Foreign Minister Bob Carr said the bombing on August 15 followed an earlier car bomb attack on July 9 and a rocket attack on May 26, targeting southern Beirut communities.

"These are barbaric attacks on civilian communities," Senator Carr said in a statement on Saturday.

"Our embassy in Lebanon has been in touch with the Lebanese government to offer condolences for the families of those killed in this latest bombing.

"As there is a risk of further attacks, Australians are advised not to travel to Beirut's southern suburbs."

Senator Carr said people already in southern Beirut should consider leaving.

Australians who are unable to contact friends or family in southern Beirut and have concerns for their safety, should contact the Department of Foreign Affairs Consular Centre on 1300 555 135.