The death toll from Saturday's truck bomb blast in Somalia's capital, Mogadishu, has surged to at least 231 people, according to police and medical sources.

At least 275 people were also wounded in the powerful explosion at a busy road junction, which flattened nearby homes and businesses and turned vehicles into burned wrecks.

Senior police officer Ali Hassan Kulmiye on Sunday confirmed the death toll to dpa news agency, with Madina Hospital Director Mohamed Yusuf counting 221 people killed and officials at Erdogan Hospital saying that there were another 10 victims from the blast.

Senator Abshir Abdi Ahmed also gave a death toll of 231, citing doctors at hospitals he had visited in Mogadishu on Sunday, according to The Associated Press news agency. Many of the bodies in hospital mortuaries had not yet been identified, he added.

Earlier in the day, Abdulkadir Abdirahman, director of the city's ambulance service, told Al Jazeera that at least 85 people were killed in the attack, warning that the death toll was expected to rise.

President Mohamed Abdullahi Mohamed Farmaajo on Sunday declared three days of national mourning following the attack.

"We will observe three days of mourning for innocent victims, flags will be flown at half-mast. Time to unite and pray together. Terror won't win," Mohamed said in a statement posted on the presidency's official Twitter account early on Sunday.

The president also urged residents to help those affected by the attack.

"I call on our citizens to come out, extend help, donate blood and comfort the bereaved. Let's get through this together," Mohamed said.

The blast, described by Mogadishu residents as the most powerful they had witnessed in years, also left dozens wounded.

No group has claimed responsibility for the attack.

Emergency services were overstretched and worked late into the night as they tried to rescue people who were trapped in the destroyed buildings.

The city's mayor called on residents to donate blood as hospitals were running out of blood.

"I call on the Somali people to visit the city's hospitals and donate blood. Please, come to the rescue of your brothers," Thabit Abdi Mohammed, told reporters after donating blood at a local hospital.

The attack came 48 hours after both the defence minister and army chief of the country resigned from their posts without explanation.

PHOTO CAPTION