ROME — The arrival of hundreds of migrants crammed into a rickety fishing boat has worsened the severe overcrowding at shelters on a tiny Italian island, triggering an angry demonstration by islanders and a vow Sunday by the mayor to call a protest strike.

While tensions grew on the Mediterranean island of Lampedusa, another migrant drama was reported. RAI state TV said a fire broke out on a small migrant boat off the coast of Calabria, on the mainland, just as the passengers were being transferred to an Italian military boat.

RAI said fuel on the migrant boat apparently caused a fire, then an explosion, and migrants ended up in the sea near Crotone. Crews from the Italian coast guard and custom boats rescued most of them, but six persons were missing, the state TV report said.

The Italian news agency LaPresse said about 20 migrants had been aboard the boat. Two customs police were reported injured.

Bathers at a beach near Crotone watched dark smoke pour out of the vessel a few miles offshore.

On Lampedusa, a migrant center meant to house fewer than 200 was now crammed with 1,200 people after the latest arrivals, including several small boats with migrants that set out apparently from Tunisia and reached the island without needing rescue.

Lampedusa Mayor Toto’ Martello expressed astonishment that a fishing boat carrying 450 migrants managed to arrive within a few miles of the island without being noticed by military vessels or aircraft, including from the European Frontex mission, which is supposed to be fighting human trafficking in the central Mediterranean.

The Italian coast guard escorted the fishing vessel to port Saturday night, where Lampedusa residents staged a protest, with some lying down, yelling “Enough!”

“Last night was a sit-in but I will call a strike” this week, with storekeepers shuttering shops for a day on the island, which lives off tourism and fishing, Martello said. The strike is aimed “against a government which doesn’t have a strategy” to deal with migrants, he said.

A week earlier, citing concern over COVID-19 infections, Sicily’s governor ordered migrant processing centers on the large Mediterranean island to shut down. But the center-left Italian government, which is in charge of migrant policy nationwide, went to court and the governor’s order was stayed, pending a hearing next month.

With so many migrants on Lampedusa, a Catholic parish stepped in to find housing for the latest several hundred arrivals.

Also reaching Lampedusa on Saturday were 49 migrants whom the Italian coast guard took from a dangerously overcrowded rescue boat, the Louise Michel, which took on so many people it couldn’t navigate. The Louise Michel’s operation is funded by street artist Banksy, who also painted the vessel a bright pink, including a lifesaving buoy in the shape of a heart.

The Louise Michel was still at sea, as were other private rescue boats, appealing for permission from either Italy or Malta to disembark hundreds of migrants they collectively have aboard, many who have been stuck for days or weeks.