Four of Greece's five new migrant registration centres are "ready to function and welcome refugees", Defence Minister Panos Kammenos said Tuesday, as Athens comes under intense pressure to control the massive influx to Europe.

The four long-delayed "hotspot" centres will open on the islands of Lesbos, Chios, Leros and Samos, which have been struggling to cope with a relentless flow of migrants landing from Turkey.

A fifth centre on the island of Kos, will be ready "in five days" despite strong opposition from the local mayor and residents over the impact on the tourism industry, Kammenos told reporters in Athens.