Six migrants, including a baby, drowned in the Aegean Sea on Friday when a dinghy carrying them sank off the Greek island of Chios, state broadcaster ERT reported, citing Greece's coastguard.

A ferry passing nearby rescued 12 people from the sunken vessel. The coastguard said it believes a trafficker was also among those who drowned.

The dinghy set off from the Turkish coast and had attempted to reach the Inousses islets near Chios, some 15 kilometres north. The nationality of the migrants was not immediately known.

The group was a part of a growing wave of refugees and migrants trying to reach wealthy European countries through the so-called Balkan route, which has been formally closed since March 2016.

Most of the migrants risk their lives to travel across the Aegean. According to the UN refugee agency, the UNHCR, 174 people drowned making the journey last year.

The pace of arrivals accelerated this year: 41,940 people arrived from January 1 until September 22, compared to 27,718 and 32,494 in the whole of 2017 and 2018, respectively, according to UNHCR figures.

Coupled with slow processing of asylum applications, the increase has led to dramatic overcrowding in refugee centres on the Greek Aegean islands. An estimated 29,000 migrants are waiting for processing on Lesbos, Chios, Samos, Leros and Kos, with the camps built for just around 6,000.

Greece's new conservative government plans to ease the overcrowding by transferring people to the mainland. Authorities shipped one group of migrants, mostly families, from the centres to the mainland earlier this month, but plan to move another 10,000.