Muhidin Ali, a Mogadishu resident who was close by at the time said it was, "the biggest blast I have ever witnessed, it destroyed the whole area". Security forces have sealed off the blast site for investigation, Mohamed said.
The blast on Saturday, in the central city's K5 Junction which is lined with government offices, hotels and restaurants, destroyed several buildings and set dozens of vehicles on fire.
The explosion left at least 20 people dead and 15 others injured. Another witness said there was a traffic jam and that the area was packed with people and cars when it happened. The explosion reportedly happened near the entrance of the hotel.
No terrorist group has claimed responsibility for the attack, though al Shabab, an offshoot of al Qaida, has carried out other auto bombings in the country in recent months.
Police now say the attacks have killed at least 30 people.
Facebook to help investigators release Russia-backed ads
Twitter took down the video, saying a remark Blackburn made about opposing abortion was inflammatory, but later recanted. One member of Congress who viewed the ads said that of about 70 that person had viewed, all of them had racial themes.
The blast at KM4 street in Hodan district occurred two days after the head of the US Africa Command was in Mogadishu to meet with Somalia's president.
Shortly after the first blast the second explosion was reported in Mogadishu's Wadajir disctict.
Somalia's defence minister and army chief have both resigned, without explaining why, in a potential blow to the government's fight against Shabaab Islamist militants.
The U.S. military has stepped up drone strikes and other efforts this year against the al-Qaida-linked al-Shabab, which is also fighting the Somali military and over 20,000 African Union forces in the country.