At least 47 people have been killed by a truck bomb targeting a police training centre in the western Libyan city of Zliten, reports say.
Media in Libya said the attack struck the al-Jahfal training camp.
The camp was a military base during the rule of ousted Libyan leader Muammar Gaddafi.
In a separate attack, a suicide bomber killed six people at the entrance to Ras Lanuf, a major oil port in northern Libya.
One of those killed was a 16-month-old child, according to Osama al-Hodeiri, a spokesman for the security forces that guard the oil facilities.
"A driver in a Toyota Land Cruiser blew himself up at a checkpoint at the entrance to the town of Ras Lanuf," he said, adding that three guards had also been killed.
Libya has been hit by instability since Gaddafi's overthrow and killing in 2011, and there is concern the so-called Islamic State (IS) group is gaining a foothold there.
The country has been run by two governments - only one of which is recognised by the international community.
A spokesman for the ministry of health of the rival government based in the capital, Tripoli, told the BBC that 47 people were killed and more than 100 people were injured in the first attack, which was reportedly heard 60km (40 miles) away in Misrata.
Other news agencies have put the death toll at 50.
Analysis: Rana Jawad, BBC News
This is one of the deadliest bomb attacks in Libya and comes at a time when hospitals across the country are suffering from severe shortages in medical supplies.
The explosion was similar in size and impact to the multiple bombings in the eastern town of al-Qubbah that targeted a petrol station in February last year.
That incident was claimed by the so-called Islamic State group, just a few months after it established a foothold in the country.
The latest explosion has not been officially claimed by any group yet, but it comes against the backdrop of intensified attacks this week carried out by IS militants near Libya's eastern oil ports.
If nothing else, the latest bombing is an indication of how the political and military chaos is degrading the institutional capabilities in the country.
Devastating attacks of this kind are on the rise, as the ability to prevent them and deal with the aftermath is at an all-time low.
It was reported that a water truck rigged with explosives was used in the bombing.
State of emergency
The ministry of health declared a state of emergency and called on all hospitals in Tripoli, 160km (100 miles) to the west of Zliten, and Misrata to the east, to take in casualties.
Residents in Zliten told the BBC that dozens of people were transferred to Tripoli, as the hospital in Zliten struggled to cope with the number of people injured.
Urgent calls for blood donations were made to Zliten residents, the Lana news agency reports.
The UN Special Representative to Libya, Martin Kobler, said that the blast was a suicide attack.
Libyan media said hundreds of recruits were outside performing morning exercises when the centre was targeted.
In December, the country's rival politicians signed a UN-brokered deal to form a unity government, but that has not yet been implemented.