An explosion ripped through a steel plant in western Turkey on Monday, killing 17 people, with President Recep Tayyip Erdogan vowing to find out who was responsible.
The blast occurred around midday (0900 GMT) at the HABAS steel factory about 60 kilometres (37 miles) north of the port city of Izmir, officials said.
"Sixteen people lost their lives in the explosion, while 13 others are receiving medical treatment, two of whom are in critical condition," Erdogan said.
"The circumstances surrounding this tragic incident ... how and why it happened, whether there was any negligence and who bears responsibility, will be established."
Health Minister Kemal Memisoglu later updated the figure to 17 after one of those in critical condition succumbed to his injuries.
Footage from the site showed a huge cloud of thick smoke pouring into the sky as flames appeared to engulf a tall structure within the HABAS Demir Celik plant in Aliaga.
Izmir governor Suleyman Elban said the explosion occurred during "a boiler replacement operation" when an overhead crane collapsed into a large industrial furnace used during the liquid steel casting process.
Speaking to AFP, 52-year-old worker Yasin Cetiner said the crane had dropped a huge container of molten steel.
"The crane rope broke, and as a result, about 120 tonnes of liquid steel fell onto the furnace. Because there are water-cooled panels inside the furnace, the liquid steel caused a hydrogen explosion when it came into contact with the water beneath it," he said.
"If the liquid steel falls on water, and it's 1,800 degrees, a massive explosion happens."
Eyewitness Deniz Ulker told AFP it felt like an "earthquake".
"There was a massive explosion... Then I looked across at the factory, and there was thick smoke coming from the chimney and giant flames," she said.
"The roof of the factory was literally flowing like water as it burned. Those flames... were flowing down. It was like doomsday."
- Relative 'set himself alight' -
HABAS is a privately owned conglomerate and one of Turkey's top steel producers. Workers' groups say it has a chequered safety record.
Turkey's pro-Kurdish DEM party said those responsible must be brought to justice.
"The workers' massacre in Aliaga is unacceptable!" it said in a statement, indicating several workers had lost their lives at the site earlier in the year "as a result of negligence".
"The causes of the explosion, any negligence and lack of oversight must be brought to light transparently, and not a single responsible party must go unpunished," DEM said, indicating its co-chair Tulay Haimogullari would visit the site on Tuesday morning and give a news conference.
Contacted by an AFP journalist, HABAS declined to answer questions.
Meanwhile, the left-wing Evrensel daily said anti-riot police were deployed outside Aliaga hospital where the wounded were being treated and had "blocked access to the site".
It also said the brother of one of those who had died in the blast had set himself alight outside the factory in protest, with onlookers intervening and taking him to hospital.
It was not immediately clear what condition he was in, but an AFP correspondent said the atmosphere outside both the hospital and the factory was very tense.
- 'We don't want to die!' -
Earlier, two representatives of the leftist Aegean Workers' Collective were arrested outside the hospital while trying to make a statement about workplace safety issues, a group spokesman said.
"The HABAS management's blind greed for profit has resulted in a major disaster today," their spokesman Oktay Turk told AFP.
"Those responsible for this massacre must be brought to justice," he said, calling for the immediate release of his colleagues.
Before Monday's explosion, Evrensel said at least 11 workers had died over the past decade while working there, and the Labour Party, a small Marxist faction, said it was the third time in three weeks that workers had lost their lives at HABAS.
Angry workers called for a protest over work safety issues at a square in Aliaga on Tuesday evening under the banner: "Enough is enough, we do not want to die!"
"We are coming together to say STOP this hell of exploitation in which dozens of our comrades have lost their lives and hundreds have been left disabled because of employers’ greed for profit!" it said.
