More than 70 people are missing in the Mediterranean after a boat crowded with migrants headed for Europe from Libya sank off neighbouring Tunisia, the coastguard said Wednesday.

The boat, which was carrying around 100 people when it put to sea, capsized off the Tunisian port of Sfax, with coastguard and navy units able to pull 24 people out of the water, National Guard spokesman Houcem Eddine Jebabli said.

"According to preliminary results of the investigation, an inflatable boat left the coast of Zawara in Libya on Sunday night with around 100 people on board," he said, adding that so far one body had been recovered. 

They were "of various African and Asian nationalities", he added.

Libya has become a major launchpad for migrants seeking to reach Europe on what has become the world's deadliest migration route.

Many end up in Italy, some 300 kilometres (180 miles) away, but many others die at sea when their often unseaworthy boats capsize or break down.

Improving weather in recent weeks has prompted a spike in departures.

Since the start of the year, 6,340 migrants have been intercepted and returned to Libya, according to figures published by International Organization for Migration (IOM) on Monday.

Human rights groups say those returned often face horrific abuses.

At least 129 people have died attempting the crossing and 459 have gone missing, the IOM said.

Tunisia's Sfax region is itself a busy departure point for attempts to reach Europe, some of them by its own citizens. 

In early May, authorities said they had found the bodies of 24 migrants who had drowned in such attempts.

Last year, 15,671 migrants attempted to reach Italy from Tunisia, up from fewer than 13,000 in 2020, according to the Tunisian Forum for Economic and Social Rights (FTDES).

Nearly 2,000 migrants went missing or drowned in the Mediterranean in 2021, compared to 1,401 the previous year, according to the IOM.