"We appeal for the international community, Somali brothers, and other Muslim brothers and or partners to send doctors to Somalia to help the hospitals treat the wounded people," President Hassan Sheikh Mohamud said in a statement on Sunday.
Health minister Ali Haji Aden said Monday the death toll now stood at at least 120, while a further 150 people were being treated in hospital.
The Somali President said his nation's ill-equipped hospitals were swamped.
"We cannot airlift all these numbers of wounded people... anyone who can send us (help) we request to send us," said Mohamud.
The World Health Organization said on Sunday it was ready to help the government treat the wounded and provide trauma care.
Bulldozers were still clearing the blast site by the Education Ministry in the capital Mogadishu on Monday in the hunt for bodies feared trapped under the rubble.
Ali Yare Ali, a local government official there told reporters that between seven and nine bodies were suspected to be under the remains of buildings destroyed by the blasts.
Saturday's attack, which also wounded more than 300 people, was claimed by the Al-Shabaab jihadist group and was the deadliest in the fragile Horn of Africa nation in five years.
It was not immediately clear how the cars loaded with explosives evaded the numerous checkpoints that ring-fence the coastal city.
Witnesses said the road was busy with rows of tuk-tuks and other vehicles when the first blast hit.
First responders were met with a second explosion, killing the elderly and women with children strapped on their back, police said.
Prime Minister Hamza Abdi Barre has ordered schools closed so that students can take part in a national blood donation drive.
Mohamud said he himself was among several hundred people who had donated blood to hospitals for the victims.
Al-Shabaab fighters have stepped up their attacks in Somalia since Mohamud was elected in May and vowed an "all-out-war" on the Islamists.
In August, the group launched a 30-hour gun and bomb attack on the popular Hayat hotel in Mogadishu, killing 21 people and wounding 117.
The insurgents have been seeking to overthrow the fragile foreign-backed government in Mogadishu for about 15 years.