At least 20 people are believed to have been killed and hundreds injured in two powerful explosions in the northern Lebanese city of Tripoli.

The blasts occurred outside two mosques on the Muslim day of prayer, when the buildings are likely to have been packed.

The first explosion happened near Taqwa mosque, close to the home of outgoing Prime Minister Najib Mikati - although his office said he was not in the city at the time.

It was followed minutes later by a second blast outside Salam mosque near the home of former police chief Ashraf Rifi.

Television pictures showed a column of thick, grey smoke rising over the city, with reports suggesting the blasts caused significant damage.

More than 20 people were killed and at least 213 injured, Lebanese health minister Ali Hassan Khalil told local TV channel Al Jadeed.

The explosions come a week after a suicide car bombing in Beirut killed 27 people. That blast ripped through a stronghold of the Lebanese Shiite group Hizbollah, which is fighting in Syria alongside forces loyal to President Bashar al Assad.

In July, a car bomb exploded in the nearby Beir al Abed district, wounding more than 50 people.