A speedboat collided with a tourist vessel off the Greek island of Aegina near Athens Tuesday, killing four people, including a child, and injuring at least another four, the coast guard said.

A total of 21 people, including the injured, were rescued from the waters between Aegina and the small deserted islet of Moni, where the tourist boat was transporting holiday-makers for a swim, the coast guard said. A search and rescue operation involving patrol boats, a helicopter and nearby private vessels was continuing to locate more possible survivors.

More than 20 people were believed to have been on board the tourist boat when it sank, but authorities said the precise number and details of how the accident occurred were unclear as rescue efforts were focused on locating survivors. It was also unclear how many people had been on board the speedboat, or what the nationalities of the survivors were.

Four bodies were recovered from the water: three men, one of them believed to have been the tourist boat captain, and that of a 9-year-old child.

Aegina's proximity to the Greek capital makes it a popular destination for Greeks and foreign tourists. Small tourist boats ferry holiday-makers from the island's port village of Perdika to Moni, an islet inhabited by deer and peacocks, and which features a popular sandy cove.