"The lack of concern that we see in many countries for the suffering and exploitation of such desperate people is deeply shocking," UN High Commissioner Zeid Ra'ad Al Hussein said at the start of talks on the issue in Geneva.
He added: "Rich countries must not become gated communities, their people averting their eyes from the bloodstains in the driveway."
A record 348,000 migrants and refugees took to leaky boats this year in search of a better life in Europe, South-East Asia, the Caribbean and the Middle East, 4,272 of them dying in the process, according to the UN refugee agency.
Most of these were in the Mediterranean, where more than 207,000 made the crossing since January, almost three times the previous high of 70,000 during the Libyan civil war in 2011. A record 3,419 lost their lives.
For the first time in decades, almost half of those hoping to make it to Europe are refugees rather than economic migrants, including 60,051 Syrians and 34,561 Eritreans.
Others — men, women and children — are being driven by lack of jobs, food and water, as well as natural disasters.
"If entire families are risking their lives at sea today, it's because they have already lost everything else and see no other option to find safety," said the UN's High Commissioner for Refugees Antonio Guterres.
"In their place we would probably do the same thing," added Zeid.
'Sea of death'
Many of those crossing the Mediterranean are towed on overcrowded boats behind "mother ships", which abandon them miles off the coast of Italy to sink or be rescued.
The Italian navy saved about 160,000 people under its Mare Nostrum search-and-rescue operation, which ran between October 2013 and October this year, admiral Giuseppe De Giorgi told delegates.
Rome ended the operation after fellow EU nations refused to help fund it, handing over to a more limited EU-run search and rescue mission known as Triton.
Some critics argued that saving the migrants was simply encouraging them to try their luck.
De Giorgi, the commander of the Italian navy, said his forces would continue to pursue smugglers.
"The Mediterranean Sea must not become a sea of death," he told delegates, calling for tougher measures against traffickers as well as more help for destination countries.
Address the root causes
Guterres convened the two-day meeting involving governments, NGOs and shipping groups in a bid to find ways to stop so many people taking to the seas.
He said cracking down on traffickers was not enough — efforts must also increase to address the reasons why people are fleeing their homes, and to improve the official channels through which they can move countries.
An arc of conflict around Europe's southern, eastern and southeastern borders, in Libya, Ukraine, Syria and Iraq, is one reason so many people are heading to the continent.
At the same time anti-immigration rhetoric is growing across the EU, fuelled by concerns about faltering economic growth and prompting calls for tougher border controls.
"At a time when an unprecedented number of people are forced to flee conflict and persecution across the world, barring them from accessing protection further afield is the opposite of what is needed," Guterres warned.
He said: "Any effective response must also address the root causes of this phenomenon."
While the Mediterranean is the most deadly route, it is by no means the only one.
At least 242 people died in the Red Sea and Gulf of Aden out of 82,680 people making the journey, most of them travelling from Ethiopia and Somalia to Yemen or onwards to Saudi Arabia or the Gulf states, the UNHCR said.
About 540 people also died this year crossing the Bay of Bengal, out of a total of 54,000 making the journey, while another 71 deaths out of 4,775 crossings were reported in the Caribbean, the UNHCR said.