Athens, Greece - Greek authorities believe more than 500 people could have died after a migrant boat capsized, with media reports on Thursday saying many of the dead could be children.

The 104 survivors from the accident some 55 miles off the south-western coast of Greece on Wednesday are being brought to a refugee camp near Athens on Thursday and Friday.

Around 26 of them are first being treated in hospital, mainly for hypothermia, authorities said.

The transfer of the dead to Athens has also begun, state broadcaster ERT reported.

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DNA samples are to be taken to identify the 78 bodies recovered.

Search efforts continued through the night and continued on Thursday, but to no avail.

"Neither survivors nor further victims were discovered during the night," a spokesperson for the Greek coastguard told state radio.

He said it is assumed that the people below deck were unable to save themselves when the 100-foot-long, rusting vessel sank.

Greek officials put the actual number of fatalities at more than 500 but say they will never be certain. The figures are based on information from survivors as well as estimates from the coastguard as to how many people were crammed onto the fishing boat.

Media reports have quoted some survivors as saying more than 700 could have been on board and that around 100 children were in the hold.

The boat had set sail from Libya days earlier, heading for Italy.

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Both coastguard officials and passing freighters radioed to help, the Greek coastguard said, adding that passengers refused assistance, saying they wanted to reach Italy.

As the boat was in international waters, the Greek coastguard could only intervene when it got into distress and capsized on Wednesday.