Driver fatigue has also emerged as a possible contributing factor.
Victoria Police Chief Commissioner Christine Nixon said the cause of the crash has not yet been established, but it appears the bus was overtaking a second busload of people on the tour when it overturned.
"The police are investigating in Egypt but it appears from a well-informed source that the buses were returning late from an outing which had started early in the morning," she said.
"Certainly from the contacts we have had it was horrendous, the accident," she said.
Ms Nixon said there have been suggestions that driver fatigue may have been a factor, as the tour had been on the road since five that morning.
The bus overturned in wet weather on a road about 8.45pm Tuesday evening local time (5.45am AEDT Wednesday) about 50 kilometres north of Egyptian capital Cairo.
The bus was one of two carrying a tour group of 80 Australia police, emergency service workers and their relatives from Alexandria to Cairo.
Five of those killed are from the south-eastern Australian state of Victoria.
Others on the tour were from Queensland and the Northern Territory.
Names released
Those killed in the accident include:
- Drew Ritchie, 14, of Wedderburn, Victoria
- Mark Ritchie, Drew's father, also of Wedderburn, Victoria, and a coordinator at Bendigo Senior Secondary College
- Senior Constable Kristy Olsen, of Moe Police, Victoria
- Sergeant George Panayiotis, who worked with the radio and electronics unit in Melbourne
- An unnamed 68-year-old man from the Melbourne suburb of Balwyn
- Luciano Prenner, 56, of Brisbane
Foreign Affairs Minister Alexander Downer earlier confirmed that two police officers and a child were among the Australians killed.
Injured treated
Egypt’s official Mena news agency said 24 of the 27 people injured are Australians.
The Egyptian driver of the bus, Mahmud Mohammed Hafez, was also hurt.
Among the Australians injured are Victorian police commander Ashley Dickinson and Northern Territory Senior Constable Carmen Butcher, 29, who was injured while helping victims.
They were initially taken to Cairo's Al-Haram hospital before being transferred to the Dar el-Fuad hospital, on the city's outskirts, except one person who was in critical condition.
Mr Downer told television station Channel Nine that four Australians are critically injured and there are serious concerns for one of them.
“The one who is seriously injured about whom we have very real concerns is in another hospital, in the initial hospital they were sent to after the crash took place and her condition is so serious that she can't be moved to the better hospital that the other injured are in. Her situation is, is very bad,” he said.
Witness accounts
Witnesses at the crash site described a scene of carnage and said the bus lay on its side on the desert highway, its roof peeled away like a sardine can by rescue workers attempting to pull out victims.
"Everybody tried to help the injured people. We put blankets around those who were cold. We tried to get them out of the rain," 65-year-old Canadian nuclear scientist Yang Albeit, who was on the second bus with his son, told The Associated Press.
Exchange tour
The Australians were part of a convoy of two buses returning from a visit to the El Alamein battlefield near Alexandria.
They were in Egypt as part of a cultural and professional exchange with Egyptian police.
A senior Victorian police officer, Commander Jim Hart, left Melbourne Airport on a flight to Cairo late on Wednesday night to provide support and assist consular officials in Egypt.
Australian Department of Foreign Affairs and Trade has set up a hotline number: 1800 002 214