Bad weather conditions and waves reaching up to three meters (10 feet) in height were hampering the rescue vessels carrying over 600 migrants to Spain, a volunteer on board the Aquarius told EFE Thursday.

The Aquarius rescue vessel belonging to SOS Méditerranée had been at sea in the Mediterranean for days following a diplomatic spat between Italy and Malta over which country should accept the ship. Spain stepped in and offered to welcome the migrants to the eastern city of Valencia.

"We're arriving to eastern Sardinia and, as predicted, the weather conditions are very bad," SOS Méditerranée volunteer Alessandro Porro said. "It’s difficult to stay on your feet," he added.

The ship has been on its way to Spain since Tuesday evening, accompanied by two vessels belonging to Italy's Coast Guard and Navy.

The 106 passengers left on board the Aquarius after the 629 migrants were shared among the three vessels spent the night inside the ship with medication on hand to relieve symptoms of dizziness, according to Porro.

The migrants had spent five days at sea and there were still two more to go in order to reach Valencia, Porro noted.

"Dattilo, the leading Italian Coast Guard ship of our convoy, decided to change route. Aquarius will proceed along the eastern coast of Sardinia to seek shelter from bad weather, otherwise unbearable for the rescued people, already exhausted, shocked and seasick," SOS Méditerranée said in a tweet.

Aquarius set off for Valencia on Tuesday and was expected to arrive to Spain on Saturday.

It was carrying 51 women, 45 men and 10 children, while the remaining migrants were shared among the Navy’s Orione ship and Coast Guard's Dattilo.

On Wednesday, the convoy stopped off on the island of Sicily to pick up supplies for the onward journey to Spain.