More than 30 migrants died and 200 were rescued on Saturday after their boats foundered off Libya's western coast, the Libyan navy said.
The coastguard conducted two rescue operations off the city of Garabulli, 60km east of Tripoli, spokesman Colonel Abu Ajila Abdelbarri said.
He added that patrols had found 31 bodies and 60 survivors from one boat, along with a further 140 survivors from a second.
"When we arrived at the spot, we found an inflatable dinghy with several people clinging to part of it," he said. He did not specify whether any people had been reported missing.
"The weather conditions these days are favourable for sending migrants to European shores on boats that are often unseaworthy," he added.
Libyan patrol boat commander Nasser al-Ghammoudi said one of the vessels was three-quarters under water when the coastguard arrived.
If you didn’t know:
Black migrants are being auctioned off in Libya.
This is not getting enough attention. They are being treated like merchandise. If you were able to be sad and outraged in history class, you can be sad and outraged now. pic.twitter.com/Ko2qA38NA0
— Lam S. Al- (@PapillonBelier) November 18, 2017
"We looked for other survivors for more than five hours," he said. "We were able to rescue one woman after we heard her shouts."
A French NGO, SOS Mediterranee, said later on Saturday that it had rescued more than 400 people from a stricken wooden boat in international waters farther from the Libyan coast.
Other rescue operations were ongoing on Saturday evening, Italian coastguard told AFP.
Italy's coastguard, which coordinates the rescue effort in international waters, reported that a total of 1,500 people had been saved on Thursday and Friday.
The large numbers of recent days contrast with the sharp drop since mid-July in the number of migrants being brought to Italy.
On Thursday, the UNHCR put the number of arrivals at Italian ports in the previous three months at 21,666, the lowest total registered in four years for that period of the year.
The downward trend has been attributed to a controversial combination of an Italian-led boosting of the Libyan coastguard's ability to intercept boats and efforts to enlist the help of powerful militias to curb traffickers' activity.
There have also been moves to tighten Libya's southern borders, accelerate repatriations directly from Libya and measures to stem the flow of migrants from sub-Saharan Africa through transit states such as Niger and Sudan.
Those rescued by Libyan coastguard on Saturday were brought back to a naval base in Tripoli where the authorities provided them with water, food and medical care.
Black migrants sold at auction
Migrants intercepted or rescued by the Libyans are usually held in detention centres to await repatriation, but waiting times are often long and conditions deplorable.
UN human rights chief Zeid Ra'ad Al Hussein in mid-November labelled as "inhuman" European Union support for Libyan authorities to intercept migrants in the Mediterranean and return them to "horrific" prisons in Libya.
Last week, US television network CNN aired footage of an apparent slave auction in Libya where black men were presented to North African buyers as potential farmhands and sold off for as little as $400.
The United Nations has said Libya must protect vulnerable men, women and children.
"Terrorist groups such as Daesh, Boko Haram, Al-Shabaab and the Lord's Resistance Army are forcing women, boys and girls into de-humanising servitude. Committed in the shadows, these actions are serious abuses of human rights and may amount to war crimes and crimes against humanity," UN Secretary-General Antonio Guterres said.