At least 42 people were killed and hundreds more injured when two powerful car bombs exploded within minutes of each other in the northern Lebanese city of Tripoli, intensifying sectarian strife which has spilled over from neighbouring Syria.

The apparently coordinated blasts - the biggest and deadliest in Tripoli since the end of Lebanon's own civil war - struck as locals were finishing Friday prayers in the largely Sunni Muslim city.

The explosions in Tripoli, 70 km (40 miles) from the capital Beirut, came a week after a huge car bomb killed at least 24 people in an area controlled by the Shiite Muslim militant movement Hezbollah.

Lebanese officials appealed for calm after a recent resurgence of sectarian violence in Lebanon, stoked by the conflagration in Syria, where president Bashar al-Assad is fighting a largely Sunni-led rebellion.

Both Hezbollah and radical Sunni groups in Lebanon have sent fighters over the border to support opposing sides in Syria.

Key points: Car bomb blasts detonated during Friday prayers killing 42, injuring hundreds

Car bomb blasts detonated during Friday prayers killing 42, injuring hundreds Interior Ministry said one blast involved a car laden with 100 kilograms of explosives

Interior Ministry said one blast involved a car laden with 100 kilograms of explosives Blast comes amid a resurgence of sectarian violence, stoked by unrest in Syria

Blast comes amid a resurgence of sectarian violence, stoked by unrest in Syria Hezbollah and UN release statements condemning the blasts

Hezbollah and UN release statements condemning the blasts Deadliest attack in the city since the end of the Lebanon civil war

The first explosion hit the Taqwa mosque, frequented by hardline Sunni Islamists, and killed at least 14 people there, according to accounts earlier in the day.

Further deaths were reported from a second blast a few minutes later outside the al-Salam mosque, which the Interior Ministry said was hit by a car laden with 100 kilograms of explosives.

"The death toll has risen to 42," a security source told AFP news agency.

Earlier, the Lebanese Red Cross earlier said there were also at least 500 wounded, with director Georges Kettaneh adding that many of those hurt had serious burns and head wounds.

A 50-metre stretch of the road was charred black and the twisted remains of cars littered the area.

"We were just bowing down to pray for the second time and the bomb went off," 39-year-old worshipper Samir Jadool said.

"The air cleared, and I looked around me and saw bodies."

Television footage showed people running through the streets, some of them carrying bloodied victims.

Near the Taqwa mosque blast site, angry men toting AK-47 assault rifles took to the streets and fired in the air while other men threw rocks at Lebanese soldiers nearby.

Soldiers peeked out at the mosque from a nearby base but did not approach it.

United Nations secretary-general Ban Ki-moon condemned the bombings and called on all Lebanese people to "exercise restraint, to remain united, and to support their state institutions, particularly the security forces".

Warnings of 'huge, grave danger'

Witnesses at the scene of the blasts said anger was rising among locals, who were shouting out accusations that Assad's government or Hezbollah were behind the attack.

Video obtained by local news channel LBC showed the moment of the explosion at al-Salam mosque.

The blast ripped through a wall of the mosque, showering clouds of dust on people sitting on prayer mats and sending dozens running out of the building.

Sunni gunmen have sporadically clashed with fighters from the city's minority Alawite sect, an offshoot of Shiite Islam to which the Assad family belongs.

Former internal security chief Ashraf Rifi, whose home was damaged by the second blast, warned Lebanon was facing a growing threat.

"We are still in the beginning of the storm and we must remain aware and try to protect this nation," he said.

"This storm has become a huge, grave danger."

Officials in Tripoli called on the government in a joint statement to step up security in the city.

Hezbollah released a statement condemning the blasts and expressing solidarity with the victims, saying they were targets of efforts to fan more violence in Lebanon.

"We consider this the completion of an effort to plunge Lebanon into chaos and destruction," the statement said.

Hezbollah's political opponents called on the group to withdraw its forces from Syria in response to Friday's attack.

Reuters/AFP