"Many more people were wounded," the source added.
"I see seven bodies inside several burned cars," said the witness, speaking from near the Taqwa mosque where the first explosion went off.
The first blast rocked the city centre near the home of outgoing Prime Minister Najib Mikati, although his office said he was not in Tripoli at the time.The second struck near the port of the restive city with a Sunni Muslim majority, close to the home of former police chief Ashraf Rifi, a security source said.
Lebanese television channels aired footage of buildings with their fronts blown in and vehicles ablaze, as bystanders rushed to help the wounded.
Tripoli, on the Mediterranean coast, has been marred by deadly violence between Sunnis, who support the armed uprising in neighbouring Syria, and Alawites who support President Bashar al-Assad.
The explosions come a week after a suicide car bombing killed 27 people in a Beirut stronghold of the Lebanese Shiite movement Hezbollah, which is fighting alongside Assad's forces.
Several people were injured in the powerful twin explosions in north Lebanon’s Tripoli. The explosion targeted the city’s al-Taqwa Mosque.
Two explosions went off within minutes of each other in the northern Lebanese city of Tripoli on Friday, media reported.
The first blast rocked the city centre near the home of outgoing Prime Minister Najib Mikati, although his office said he was not in Tripoli at the time.
The second occurred near the port of the restive city with a Sunni Muslim majority that has been marred by deadly violence linked to the 29-month conflict in neighbouring Syria, said the National News Agency.
Voice of Russia, AFP, Reuters