Latest: 15 primary school children among those killedi n Somalia blast

Update 11.30: Fifteen primary school children were among the over 300 people killed in Somalia's deadliest blast, an ambulance service director has said.

Abdulkadir Adam said the children were on a school bus and died when the massive lorry bomb detonated nearby.

Saturday's attack struck a crowded street near some of Somalia's government ministries in the capital,Mogadishu.

About 300 people are injured, many of them badly.

Earlier: The death toll from Saturday's lorry bombing in Somalia's capital has risen to more than 300, as the country reeled from the deadliest single attack it has ever experienced.

Dr Abdulkadir Adam of Aamin Ambulance service said more people had died of their wounds in the past few hours.

Funerals began, and the death toll was expected to rise again.

Saturday's bombing targeted a crowded street in Mogadishu, and about 300 others were injured.

Somalia's government is blaming the al Qaida-linked al-Shabab extremist group, which has not commented.

Officials said more than 70 critically injured people were being airlifted to Turkey for treatment on Monday as international aid began to arrive.

Nervous relatives stood at the airport, praying for the recovery of their loved ones.

Overwhelmed hospitals in Mogadishu were struggling to help other badly wounded victims, many burned beyond recognition.

The attack was one of the worst in the world in recent years.

It was one of the deadliest attacks in sub-Saharan Africa, larger than the Garissa University attack in Kenya in 2015 and the US Embassy bombings in Kenya and Tanzania in 1998.

Information minister Abdirahman Osman said other countries including Kenya and Ethiopia had already offered to send medical aid in response to what Somali's government has called a "national disaster".

Al-Shabab, Africa's deadliest Islamic extremist group, often targets high-profile areas of Mogadishu.

Earlier this year it vowed to step up attacks after both the Donald Trump administration in the US and Somalia's recently elected president announced new military efforts against the group.

The country's Somali-American leader, President Mohamed Abdullahi Mohamed, has declared three days of mourning and joined thousands of people who responded to a desperate plea by hospitals to donate blood.

"This is really horrendous, unlike any other time in the past," said Dr Mohamed Yusuf, the director of Medina hospital.

Exhausted doctors struggled to keep their eyes open, while screams from victims and newly-bereaved families echoed through the halls.

Mogadishu, a city long accustomed to deadly bombings by al-Shabab, was stunned by the force of Saturday's blast.

The explosion shattered hopes of recovery in an impoverished country left fragile by decades of conflict, and it again raised doubts over the government's ability to secure the seaside city of more than two million people.

The United States has condemned the bombing, saying "such cowardly attacks reinvigorate the commitment of the United States to assist our Somali and African Union partners to combat the scourge of terrorism".

It tweeted a photo of its charge d'affaires in Somalia donating blood.

But the US Africa Command said US forces had not been asked to provide aid.

The US military has stepped up drone strikes and other efforts this year against al-Shabab, which is also fighting the Somali military and more than 20,000 African Union forces in the country.

AP