There were no immediate reports of serious damage in the metropolis of 16 million.

More than 150 people were hospitalised with injuries sustained while attempting to flee buildings, the Istanbul governor’s office said.

The earthquake had a shallow depth of 10 kilometres, according to the United States Geological Survey, with its epicenter about 40 kilometres southwest of Istanbul, in the Sea of Marmara.

It was felt in the neighbouring provinces of Tekirdag, Yalova, Bursa and Balikesir and in the city of Izmir, some 550 kilometres south of Istanbul.

There were several aftershocks, including one measuring 5.3.

The incident, which started at 12.49pm (7.49pm AEST) during a public holiday when many children were out of school and celebrating in the streets, caused widespread panic in Istanbul, which is on tenterhooks due to the looming threat of a major earthquake.

Panicked residents rushed from their homes and buildings into the streets. The disaster and emergency management agency urged people to stay away from buildings.

“Due to panic, 151 of our citizens were injured from jumping from heights,” the Istanbul governor’s office said in a statement.

“Their treatments are ongoing in hospitals, and they are not in life-threatening condition.”

Many residents flocked to parks, school yards and other open areas to avoid being near buildings in case of collapse or subsequent earthquakes. Some people pitched tents in parks.

“Thank God, there does not seem to be any problems for now,” President Recep Tayyip Erdogan said at an event marking the National Sovereignty and Children’s Day holiday.

“May God protect our country and our people from all kinds of calamities, disasters, accidents and troubles.”

Leyla Ucar, a personal trainer, said she was exercising with her student on the 20th floor of a building when they felt intense shaking.

“We shook incredibly. It threw us around, we couldn’t understand what was happening, we didn’t think of an earthquake at first because of the shock of the event,” she said.

Senol Sari, a 51-year-old resident who fled to a park nearby his house, told The Associated Press he was with his children in the living room of his flat on the third floor of an apartment building when he heard a loud noise and the building started shaking.

“We immediately protected ourselves from the earthquake and waited for it to pass, then calmly walked away from the house,” Sari said.

“Of course, we were scared during the earthquake. We were worried that it would continue. Since the (great) Istanbul earthquake is (still) an expected earthquake, our concerns continue.”

‘My children were a little scared’

Cihan Boztepe, 40, was one of those who hurriedly fled to the streets with his family in order to avoid a potential collapse.

Boztepe, standing next to his sobbing child, told AP that he was living in Batman province, an area close to the southern part of Turkey where the 2023 quakes hit, and that Wednesday’s tremor felt weaker and that he wasn’t as scared.

“At first we were shaken, then it stopped, then we were shaken again. My children were a little scared, but I wasn’t. We quickly gathered our things and went down to a safe place. If it were up to me, we would have already returned home.”

Turkey’s interior minister, Ali Yerlikaya, said the authorities had not received reports of collapsed buildings. He told HaberTurk television that there had been reports of damage to buildings.

The NTV broadcaster reported that a derelict and abandoned former residential building in this historic Fatih district, which houses the Blue Mosque and the Hagia Sophia Grand Mosque, had collapsed.

Kemal Cebi, the mayor of Kucukcekmece district in western Istanbul, told NTV there were “no negative developments yet,” but reported traffic jams, and said many buildings were already at risk due to the area’s density.

In Zeytinburnu district, some people were injured after jumping out of buildings, mayor Omer Arisoy told NTV.

Urban reconstruction projects

Turkey is crossed by two major fault lines, and earthquakes are frequent.

A magnitude 7.8 earthquake on February 6, 2023, and a second powerful tremor hours later, destroyed or damaged hundreds of thousands of buildings in 11 southern and southeastern provinces, leaving more than 53,000 people dead.

Another 6000 people were killed in the northern parts of neighbouring Syria.

Istanbul was not impacted by that earthquake, but the devastation heightened fears of a similar quake, with experts citing the city’s proximity to fault lines.

In a bid to prevent damage from any future quake, the national government and local administrations started urban reconstruction projects to fortify buildings at risk and launched campaigns to demolish buildings at risk of collapse.