Italy says 4,000 immigrants have reached its shores by boat in the past two days – the highest number since it began a naval operation to handle the influx after two shipwrecks last year.

"The landings are non-stop and the emergency is increasingly glaring," the interior minister, Angelino Alfano, said.

"Right now two merchant ships are rescuing two boats with 300 and 361 people aboard. It appears there's at least one corpse on board." Alfano estimated that 15,000 migrants crossing the Mediterranean had been rescued so far this year.

He claims up to 600,000 people from Africa and the Middle East are ready to set off from Libyan shores.

"Europe must take the situation in hand. It cannot say that, having given €80m (£66m) to Frontex, the problem has been resolved," he said, referring to the European Union's border control agency.

"There are death merchants who profit from this people-trafficking and who send out requests for help just 30 to 40 miles after leaving the Libyan coasts."

Italy began its naval operation after more than 400 migrants from Eritrea and Syria perished in twin tragedies off Italian shores in October 2013.

Five navy ships are currently operating in the region south of the tiny Italian island of Lampedusa, which has become one of the biggest gateways for irregular migration into the European Union.

Italy said it had rescued around 2,500 of the 4,000 arrivals and that others were being intercepted by merchant ships and coastguard vessels.

This is the highest number over a 48-hour period since the naval operation began, a spokesperson said. Italy reported a 60% increase in asylum claims last year – mainly people fleeing the war in Syria – although numbers of arrivals are still lower than after the Arab Spring revolts in 2011.

The latest increase comes just ahead of European parliament elections next month. The anti-immigration Northern League – a small opposition party – was quick to weigh in on the issue, urging Alfano to stop the arrivals "by turning them back".

But Silvia Canciani, a spokeswoman for the Association for Legal Studies on Immigration, played down the scale of the new influx.

"The number of people arriving is increasing, but it is only becoming an emergency because of the bad management of Italy's asylum system," she said.

She said the new arrivals would probably be taken to private accommodation such as hotels "because there is no more space" in Italy's asylum and immigration centres, warning that vulnerable migrants such as minors risked not receiving the care they needed.

"This is very similar to the North Africa emergency in 2011. The Italian government is repeating the same mistakes," she said.