ISTANBUL, Turkey -- A magnitude-6.1 earthquake struck northwest Turkey during Wednesday's early hours, injuring at least 50 people.

The shallow tremor struck about 170 kilometres (105 miles) east of Istanbul, the country's largest city, where it was strongly felt.

National authorities said the quake was at a magnitude of 5.9 -- lower than the 6.1 given by the US Geological Survey -- and its epicentre was in Duzce province's Golyaka district, though it also shook other nearby cities.

"We were woken up with a big noise and tremor," Duzce resident Fatma Colak told AFP.

"We got out of our homes in panic and now we are waiting outside."

Interior Minister Suleyman Soylu, who visited Golyaka, said one person was seriously hurt after jumping from a balcony out of panic.

Initial images showed people covered in blankets outside their homes during the early morning. Some were seen placing blankets on the floor outside, and lighting fires for warmth.

Authorities said schools would be closed on Wednesday in Duzce and Sakarya provinces.

Soylu said that, apart from a few ruined barns, there were no reports of heavy damage or building collapses, but inspections were continuing.

He said authorities would check 8,000 buildings for any damage.

National disaster agency AFAD said there were controlled blackouts in the Duzce region, urging residents not to panic.

It also reported that 101 aftershocks had been recorded.

Turkey is in one of the world's most active earthquake zones.

Duzce was one of the regions hit by a 7.4-magnitude earthquake in 1999 -- the worst to hit Turkey in decades.

That quake killed more than 17,000 people, including about 1,000 in Istanbul.

Experts have long warned a large quake could devastate Istanbul, which has allowed widespread building without safety precautions.

A magnitude-6.8 quake hit Elazig in January 2020, killing more than 40 people.

And in October that year, a magnitude-7.0 quake hit the Aegean Sea, killing 114 people and wounding more than 1,000.