Family members say Laura Macintyre and Eilidh MacLeod haven't been heard from since the explosion.
Safety Review After Rally Deaths
Police will carry out a review of safety at public events in Scotland following the deaths of three people at a rally, Justice Secretary Kenny MacAskill has announced.
The Scottish Government will also commission a review of motor sport event safety in the country in light of the tragedy.
Iain Provan, 64, Elizabeth Allan, 63 and Len Stern, 71, were killed in what was the second of two crashes during the Jim Clark Rally in the Scottish Borders on Saturday afternoon.
Two other injured men, both 61, are still in hospital - one in a stable condition and one in a critical but stable condition in Edinburgh Royal Infirmary.
Mr MacAskill announced the reviews as he gave a statement to the Scottish Parliament.
"We have had discussions with Police Scotland about the need to review spectator safety more generally,'' he said.
"We are moving into an unprecedented summer, the longer nights are with us, and with this in mind I think it appropriate to review safety at public events, and to do so very speedily.
"Across the country there is a busy calendar of events and a huge amount of careful planning already done.''
He added: "While the Jim Clark rally is unique as a closed road and unticketed motor rally, the Scottish Government will ask Police Scotland to work with event organisers and local authorities to undertake a health check of event planning for events taking place this summer.
"This will ensure safety regimes and risk assessment procedures are in place, and the licensing conditions are being met.''
Mr MacAskill said the review will happen over the next four weeks, ahead of major events including the Commonwealth Games in Glasgow and the Ryder Cup at Gleneagles.
He continued: "Spectator safety must always be paramount.
"In the light of the weekend deaths the Scottish Government will commission a review of motor sport event safety in Scotland, drawing on safety experts and the knowledge and expertise of the motor sport community.''
This review will include Police Scotland, event organisers, Borders Council, the Motor Sports Association and others, and will look at the training and deployment of stewards as well as all other safety controls, Mr MacAskill told MSPs.
Commenting on the Jim Clark event, Mr MacAskill said: "In light of Saturday's events, the minister for transport will be giving careful consideration to the safety aspects of the 2015 rally and the need for conditions.
"Clearly, this decision will be dependent on the information that comes forward from the safety reviews of the event.''
He said a full police investigation, under the direction of the Crown Office, continues into the circumstances.
The decisions on holding a discretionary Fatal Accident Inquiry or pursuing any criminal prosecutions are for the Lord Advocate, Mr MacAskill said.
The fatal crash took place at about 4pm on Saturday at Little Swinton, near Coldstream.
About 250 competitors had been taking part in the rally, which is said to be one of the largest in the UK.
Thousands of spectators watched the action but it was immediately abandoned after the fatal crash.
Two hours earlier another car in the rally left the road and hit five people, one woman and four men, near Crosshall Farm on the Eccles stage of the competition.
Three of the men were taken to Borders General Hospital but one was then moved to an intensive care unit in Edinburgh. The other two spectators were treated for minor injuries.
Conservative MSP John Lamont, whose constituency takes in the rally course, said: "Our thoughts and prayers are with the victims, their families and friends, and also for those who are still in hospital.
"We should also have thought for those spectators and marshals who witnessed the horrific scenes on Saturday afternoon.
"Clearly it is welcome news that a full investigation will be carried out.
"However, can I urge caution against any kneejerk reaction in terms of how we respond to this tragedy.
"This is a long-established event in the Borders and although everyone is shocked by events at the weekend, it would be regrettable if any premature decisions were taken about the event's future.''
Liberal Democrat MSP Jim Hume asked whether counselling will be offered to people who witnesses the fatal crash.
Mr MacAskill replied: "Clearly there were people who were present who saw the tragedy unfold in front of their eyes and may very well require treatment.''
Labour MSP Graeme Pearson said: "There are no doubt pressing questions that we would all like answers to and I realise, as many will in this chamber, that we must await the outcome of the police inquiries.''
Police have set up an email address for members of the public to send any video clips they have of the rally: email@example.com.
The families of two girls from the Western Isles missing after attending the concert in Manchester targeted in a terror attack have issued appeals on social media.
Crews were called to the former Royal Victoria Hospital site this afternoon.
John Bermingham was also accused of assault and a breach of a Sexual Offences Prevention Order.
Most Viewed Pictures On Heart
Recently Played Tracks
To listen live, choose your preferred station:
Now playing: The best feel good music
Now playing: The best feel good music
Deposit £10 to get a £40 Welcome Bonus - That's £50 to play bingo, slots and more!*
Over 50 tracks to make you feel-good. New album out now...
Find your local four day weather report here.
Make Heart the soundtrack to your day and you could be a winner with great prizes up for grabs throughout the day.
Find out more about some of the companies advertising on Heart Scotland- East.