More than 350 migrants including those rescued by a vessel sponsored by British street artist Banksy were being transferred onto a quarantine vessel off Sicily, aid workers said Wednesday.

"The first people have boarded the quarantine vessel and the operation is ongoing," Mattea Weihe, spokeswoman for the Sea-Watch humanitarian organisation told AFP.

The 353 migrants on board Sea-Watch 4 include those rescued last week by Louise Michel, a 30-metre boat sponsored by the mysterious artist.

Many have been on board under severely cramped conditions for the past 12 days, Weihe added.

The migrants are due to land in Palermo, Sea Watch said, after quarantine checks.

Meanwhile at Palermo's Cervello hospital a migrant mother who tested positive for Covid-19 and her baby were undergoing treatment, Italian news agency ANSA said.

The woman went into labour at the crowded migrant holding centre on the southern island of Lampedusa on Tuesday and authorities decided it would be better to fly her to Palermo.

However, she gave birth as the helicopter neared the city of Agrigento, about 120 kilometres (75 miles) south of Palermo.

The transfers come as the latest arrivals fuel anger from local officials in Lampedusa and Sicily over a rise in illegal landings.

Italy has been struggling in recent months with daily arrivals of hundreds of migrants from North Africa, a task complicated by security measures imposed under the coronavirus crisis.

Sicily's regional governor, the right-leaning Nello Musumeci, and Lampedusa mayor Toto Martello were to meet Italian Prime Minister Guiseppe Conte on Wednesday in Rome to discuss the issue, news reports said.

The meeting comes after an Italian court last week slapped down a decree issued by Musumeci ordering the closure of migrant centres on the island to curb the spread of the coronavirus.

From August 1 last year to July 31 this year, over 21,600 migrants arrived on Italy's shores -- compared with nearly 8,700 landings the year before, official data shows.

Despite the sharp rise, migrant arrivals are still far below the numbers recorded in recent years, especially before Rome signed a deal with Libya for its coast guard to prevent migrant departures.