Two strong aftershocks have struck the Greek island of Kos within minutes of each other, sending startled residents and tourists scurrying away from homes and restaurants.

A tremor measuring a preliminary 4.4 magnitude struck at 8.09pm local time (6.09on BST), sending restaurant customers scurrying toward the middle of the town's main square, as far away as possible from buildings.

Sixteen minutes later, a second 4.6-magnitude tremor struck, the Athens Geodynamics Institute reported. The first tremor had its epicentre only 13 miles northeast of Kos at a depth of 6 miles.

Hundreds of residents and tourists spent Friday night sleeping outdoors on the island, too afraid to return to their homes or hotels after the quake that struck early on Friday, killing two men on Kos and injuring almost 500 others in Greece and Turkey.

Many camped out in parks and olive groves, or slept in their cars or on beach and swimming pool lounge chairs.

The aftershocks meant that many would spend a second night outdoors.

During the day in Kos, churches, an old mosque, the port's 14th-century castle and other old buildings that suffered in the quake were being checked by archaeologists and experts from Greece's Culture Ministry.

The US Geological Survey measured Friday's earthquake at magnitude 6.7, with Greek and Turkish estimates a fraction lower. Two men, a Turk and a Swede, were killed when a wall collapsed into a popular bar in the Old Town of Kos.

The most seriously injured in Greece were airlifted to hospitals on the mainland and the southern island of Crete, and at least two were still in critical condition on Saturday.

Two dead in earthquake that strikes Greek island of Kos

The Turkish man's parents were on the island making arrangements to repatriate his body home by boat, possibly on Sunday.

Panagiotis Bekali, a 30-year-old resident, spent the night sleeping in an olive grove with relatives while his five-year-old son and 16-year-old nephew slept in the family car.

“There were cracks in the house (from the earthquake) so we went straight out,” he said. “We were afraid to stay indoors, so the whole family slept outside.”

Dozens of aftershocks have shaken the island. John Grant, a 60-year-old tourist from Britain, said he felt safer sleeping outside.

“Coming from somewhere that doesn't have earthquakes, you don't understand,” he said from his makeshift bed on a lounge chair. “So to me it was very frightening being in the building. But being outside, I know I'm safe.”

About 350 of the injuries occurred in Turkey, in Bodrum and other beach resorts, as people fled buildings and as a sea swell flung cars off the road and pushed boats ashore. Seismologists said the shallow depth of the undersea quake Friday was to blame for the damage.

In Kos, the quake damaged the island's main port, so ferries were being diverted to the smaller port of Kefalos on the island's southwestern coast.

Serif Damadoglou Soukri, the imam of Kos, said the greatest damage to Kos mosques was sustained by the central 17th-century Defternatar Ibrahim Pasa mosque, whose minaret, restored a few years ago, collapsed completely. Ancient columns also toppled over in the southern part of the 2nd-century agora in the main town.

Earthquake rocks Turkey-Greek coasts Show all 11 1 /11 Earthquake rocks Turkey-Greek coasts Earthquake rocks Turkey-Greek coasts A man looks at damaged boats at a beach following a sea surge caused by an earthquake on July 21, 2017 in Bodrum, southwestern Turkey. Two foreigners died and more than 100 people were injured on the Greek island of Kos when an earthquake shook popular Greek and Turkish holiday destinations in the Aegean Sea. The epicentre of the 6.7 magnitude quake was some 10.3 kilometres (6.4 miles) south of the major Turkish resort of Bodrum, a magnet for holidaymakers in the summer, and 16.2 kilometres east of the island of Kos in Greece, the US Geological Survey said. AFP/Getty Images Earthquake rocks Turkey-Greek coasts A man sweeps away rubble following on the Island of Kos following a 6.5 magnitude earthquake which struck the region early on July 21, 2017. Two foreigners died and more than 100 people were injured on the Greek island of Kos when an earthquake shook popular Greek and Turkish holiday destinations in the Aegean Sea. The epicentre of the 6.7 magnitude quake was some 10.3 kilometres (6.4 miles) south of the major Turkish resort of Bodrum, a magnet for holidaymakers in the summer, and 16.2 kilometres east of the island of Kos in Greece, the US Geological Survey said. AFP/Getty Images Earthquake rocks Turkey-Greek coasts A man looks at rubble fallen from a quake damaged building on the Greek Island of Kos on July 21, 2017 following a 6.5 magnitude earthquake which struck the region. Two foreigners died and more than 100 people were injured on the Greek island of Kos when an earthquake shook popular Greek and Turkish holiday destinations in the Aegean Sea. The epicentre of the 6.7 magnitude quake was some 10.3 kilometres (6.4 miles) south of the major Turkish resort of Bodrum, a magnet for holidaymakers in the summer, and 16.2 kilometres east of the island of Kos in Greece, the US Geological Survey said. AFP/Getty Images Earthquake rocks Turkey-Greek coasts Damaged boats are seen on a beach following a sea surge caused by an earthquake, in the Agean coastal city of Mugla, Bodrum Province, Turkey Earthquakequake hits the Aegean - 21 Jul 2017 A strong 6.7 magnitude earthquake hit Turkey's Aegean coast, and at least 90 people were injured as a sea surge caused damages in buildings and streets. Two people were killed and dozens were injured on the Greek Island of Kos and beachfront hotels have been flooded on both Turkish and Greek coasts after the earthquake hit in the Aegean Sea early 21 July. Rex Features Earthquake rocks Turkey-Greek coasts Damage is seen at a port following an earthquake on the island of Kos, Greece, 21 July 2017. Two earthquake-related fatalities were reported on the island of Kos in the early morning hours of 21 July, while several others were injured from a strong 6.7 magnitude earthquake that shook the island and much of the southeast Aegean region and southwestern Turkey. A 39-year-old Turk and a 27-year-old Swede are reportedly dead, according to sources. Five persons who have been seriously injured were transferred to the Heraklion University Hospital in Crete. Some buildings have suffered serious damage. The island's port has sustained damage while the airport is operating normally. EPA Earthquake rocks Turkey-Greek coasts Boats that crashed on top of each other in the harbor in Bodrum, Turkey, early Friday, July 21, 2017. A powerful earthquake struck Turkey's Aegean coast and nearby Greek islands, sending frightened residents running out of buildings they feared would collapse and into the streets. AP Earthquake rocks Turkey-Greek coasts Fallen bottles are seen in a liquor store following an earthquake on the island of Kos, Greece, 21 July 2017. Two earthquake-related fatalities were reported on the island of Kos in the early morning hours of 21 July, while several others were injured from a strong 6.7 magnitude earthquake that shook the island and much of the southeast Aegean region and southwestern Turkey. EPA Earthquake rocks Turkey-Greek coasts People watch a damaged car following a sea surge caused by an earthquake, in the Agean coastal city of Mugla, Bodrum Province, Turkey, 21 July 2017. A strong 6.7 magnitude earthquake hit Turkey's Aegean coast, and at least 90 people were injured as a sea surge caused damages in buildings and streets. Two people were killed and dozens were injured on the Greek Island of Kos and beachfront hotels have been flooded on both Turkish and Greek coasts after the earthquake hit in the Aegean Sea early 21 July. EPA Earthquake rocks Turkey-Greek coasts Damaged boats are seen on a beach following a sea surge caused by an earthquake, in the Agean coastal city of Mugla, Bodrum Province, Turkey, 21 July 2017. A strong 6.7 magnitude earthquake hit Turkey's Aegean coast, and at least 90 people were injured as a sea surge caused damages in buildings and streets. Two people were killed and dozens were injured on the Greek Island of Kos and beachfront hotels have been flooded on both Turkish and Greek coasts after the earthquake hit in the Aegean Sea early 21 July. EPA Earthquake rocks Turkey-Greek coasts Damaged buildings are seen after an earthquake on the Greek island of Kos early Friday, July 21, 2017. A powerful earthquake struck Greek islands and Turkey's Aegean coast early Friday morning, damaging buildings and a port and killing people, authorities said. AP Earthquake rocks Turkey-Greek coasts Hotel guests sleep outdoors after abandoning their rooms following an earthquake in Bitez, a resort town about 6 kilometers (4 miles) west of Bodrum, Turkey, early Friday, July 21, 2017. A powerful earthquake struck Turkey's Aegean coast and nearby Greek islands, sending frightened residents running out of buildings they feared would collapse and into the streets. AP

Greek Orthodox Priest Vassilis Hlampanis said one of the damaged churches was repairable.

“The greatest damage was sustained mainly in part of the sanctuary, in the middle part which fell, but there are also other sections around the external brickwork and certainly also internally,” he said.

Kos Mayor Giorgos Kyritsis said island's biggest infrastructure problem was the damage to the main port. Coast guard divers were on the scene inspecting the jetty.

“Life on the island is returning to normal,” Kyritsis said. “The infrastructure problems are being repaired.”

The mayor said Kos hadn't seen many tourist cancellations as a result of the quake.

“(Visitors) are touring the island with their tour guides. We don't have a big problem. The ferry connection has been restored with the port of Kefalos and we are waiting as soon as possible to repair the damage at the port,” he said.

Gift shop owner Giannis Manoutkos said life on the island had returned to its easy-going ways.

“Everything is normal now. The situation was bad for two days ... we are coming to a normal life again,” he said.