A 6.4-magnitude earthquake rocked Turkey's southern province of Hatay and northern Syria on Monday evening, killing six people and sparking fresh panic after a massive February 6 tremor that left nearly 45,000 dead in both countries.
The AFAD disaster response agency reported the deaths as well as nearly 300 hospitalisations, while in Syria the White Helmets aid group said at least 150 people were injured in the Aleppo region, AFP reported.
Monday's quake hit the Turkish town of Defne at 8:04 pm (1704 GMT) and was strongly felt by AFP teams in the nearby city of Antakya. It was also felt in Lebanon.
Turkey's disaster management agency said on Twitter that a 5.8-magnitude quake followed three minutes later, with its epicentre in the Samandag district of Hatay province.
The agency recorded two more tremors with magnitudes of 5.2 around 20 minutes after the first on Monday.
Images from the DHA news agency showed a hospital in Antakya being evacuated, while broadcaster NTV reported that a hospital was evacuated in the city of Iskenderun.
DHA said patients in an intensive care unit were taken by ambulance to field hospitals to continue their treatment.
Soylu said rescue workers were trying to find people trapped under rubble.
An AFP journalist reported scenes of panic in Antakya, with the new tremors raising clouds of dust in the devastated city. The walls of badly damaged buildings crumbled while several people, apparently injured, called for help.
On a street in Antakya, Ali Mazlum, 18, told AFP: "We were with AFAD who were looking for the bodies of our family when the quake hit.
"You don't know what to do... we grabbed each other and right in front of us, the walls started to fall. It felt like the earth was opening up to swallow us up."
Mazlum, who has lived in Antakya for 12 years, was looking for the bodies of his sister and her family as well as his brother-in-law and his family.
"The road moved like waves. The building moved back and forth, the cars moved left to right. It knocked me off my feet," said Mehmet Irmak, who works at a notary's office in Antakya.
"Hatay is no longer a safe place. We could hear a lot of buildings collapsing... We will wait for a new day, but I don't know what I'm going to do," added Irmak, who had been sleeping in his car for two weeks after the first quake.
The Syrian American Medical Society (SAMS) said five hospitals it supports in northwest Syria received several people who had sustained minor injuries, some when parts of damaged buildings fell on them.
In government-held areas of Syria, Aleppo hospitals also received panic-stricken residents, while six people were injured by falling rubble, the state news agency SANA said.
Al Razi hospital in Aleppo received 47 cases, state media reported.
"We rushed out, we don't know how we left. I was afraid that we would meet the same fate as those who died under the rubble," said Khadija Al Khalaf, a 45-year-old mother, in the rebel-held city of Azaz.
According to AFAD, more than 6,200 aftershocks have been recorded since the 7.8-magnitude hit Turkey and Syria on February 6, leaving millions homeless.
Officials said after the quake that aftershocks would be felt for a year because of the force of the first tremor.
Officials have set the death count from that quake at 41,156 people in Turkey and 3,688 in Syria, but experts say the number will rise as the rubble is cleared and rescue operations end.
Eleven provinces in Turkey were hit by the previous tremors and on Sunday, officials said rescue operations would continue in only two: Hatay and Kahramanmaras.
"My thoughts continue to be with the people of Turkiye and Syria, as they face the impact of new earthquakes striking the region this evening," wrote UN chief Antonio Guterres on Twitter.
UN teams there "are assessing the situation, and we stand ready to provide additional support as needed", he said.
Earlier on Monday, US Secretary of State Antony Blinken held talks in Ankara with Turkish President Recep Tayyip Erdogan and Foreign Minister Mevlut Cavusoglu, as he wrapped up a visit during which he pledged solidarity after the tremors.
The United States has contributed USD 185 million in assistance to Turkey and Syria.