A photograph showing the body of a man found dead in a rubber dinghy at sea lays bare the horrific risks taken by those trying to cross the Mediterranean into Europe.

Armed Forces Malta released the image on Tuesday after a maritime rescue mission found one man dead and another in a critical condition. 

The picture shows the barely-clothed dead body of the man with his companion kneeling over him in their small boat in the searing heat. There is no sign of food or water.

It comes as the UN warns of a "race against time" for some 507 other migrants stranded on board two rescue ships with nowhere to go.

Both men were trying to cross the Mediterranean into Europe on board the blue rubber boat when they were found on Monday.

Home Affairs minister Michael Farrugia said the survivor was found "lying over the corpse" of his companion.

"This is what Armed Forces Malta do each and every day. We cannot do this alone."

It is not known how the man died. His rescued companion was taken to the Air Wing Base by helicopter and later hospitalised.

By the time the AFM rescue team had arrived, the man was already dead. A spokeswoman said on Tuesday morning that his body was being transferred to land by patrol boat. 

"The Armed Forces of Malta is now releasing a photo of yesterday’s rescue operation of 2 persons on board a rubber boat," it said.

"While the first casualty was found to be in critical condition and brought to Malta by AFM’s AW139 helicopter, the second person resulted dead and is being transferred to Malta by the AFM’s P52."

'Race against time' for 507 stuck at sea

More than 600 people have died while crossing the Mediterranean in the first six months of the year, according to the United Nations' International Organisation for Migration.

The latest death comes as NGOs operating rescue vessels across central Mediterranean routes repeatedly clash with EU member states which have been reluctant to allow them in. 

Some 507 migrants aboard two ships are currently stranded with nowhere to disembark.

The Ocean Viking, currently has 356 rescued people aboard and nowhere to take them. Another vessel, the Open Arms, is carrying a further 151 people who have been denied entry into European ports. 

On Tuesday the UN's Refugee Agency called for European governments to allow them into the ports.

"This is a race against time," said Vincent Cochetal, UNHCR Special Envoy for the Central Mediterranean.

"Storms are coming and conditions are only going to get worse."

On Monday, president emeritus Marie-Louise Coleiro Preca said European politicians "should be ashamed of themselves" for their refusal to allow rescued people onto land. 

A European Commission spokeswoman told Times of Malta that neither Malta nor any other member state had made a formal request for the EU to mediate a potential solidarity effort to resolve the crisis.