* Thirty-eight people still missing
* Putin visits mine, orders probe
* Time running out to find survivors
* Raspadskaya shares fall on opening
(Edits, adds more analyst comments)
By Darya Korsunskaya
MEZHDURECHENSK, Russia, May 11 (Reuters) - The death toll from a Siberian coal mine disaster at the weekend rose to 52 on Tuesday and dozens of workers were still missing in a maze of tunnels threatened by flooding, emergency officials said.
"Thirty-eight people are still missing," an Emergencies Ministry spokeswoman said. Asked if there was a hope to find any survivors, she said: "Rescue and recovery works continue non-stop, round-the-clock." She gave no further detail.
As hopes faded for those trapped underground after Russia's worst mine accident in three years, Prime Minister Vladimir Putin met grieving relatives and injured survivors in a region that lives on coal.
Putin then walked above the Raspadskaya mine, where emergency workers used heavy machinery and their bare hands to dig through the rubble of a wrecked building.
"I order the most detailed investigation into the causes of the accident, the situation at the mine and the actions of specific authorities," Putin, dressed in black, sternly told officials in televised remarks.
"We need to know what led to such a large number of casualties - to a tragedy of such scale," he said.
Putin said lessons must be learnt to create "systemic solutions aimed at avoiding a repeat of such tragedies" across Russia's accident-prone coal industry.
Shares in mine owner Raspadskaya
, Russia's largest stand-along coking coal producer, plunged 15 percent at the start of the first day of trade after the weekend disaster. The fall deepened to 16.53 percent by 11.50 GMT.
More than 350 miners were underground when a blast hit the mine in Mezhdurechensk, about 3,000 km (1,850 miles) east of Moscow, at the weekend.
Many managed to escape, but a second blast hours later trapped others and damaged buildings on the surface, including a main ventilation shaft.
Aman Tuleyev, governor of the Kemerovo region, said time was running out to rescue those trapped in areas of the mine where anti-flooding systems had failed.
Valery Korchagin, Emergencies Ministry spokesman in the region, said 19 of the dead were rescuers who went into the sprawling mine after the initial blast.
"When you have lost a loved one, it is so terrible and so tragic that no words of condolence are fitting," Putin told relatives of the dead before visiting the mine. "I want you to know, we all want you to know, that you are not alone."
News agencies have quoted Emergencies Minister Sergei Shoigu as saying that a sudden burst of methane and coal dust could have caused the blasts.
The mine disaster unfolded as Putin and President Dmitry Medvedev hosted foreign leaders and honoured veterans in huge celebrations on Sunday marking the 65th anniversary of the World War Two defeat of Nazi Germany.
"Nobody can be forgotten," Putin said of the mine-blast victims and their relatives, echoing a slogan used to honour those who fought in what Russians call the Great Patriotic War.
Mine explosions and other industrial accidents have prompted repeated calls from Russia's leaders for improvements to creaking infrastructure and stricter adherence to safety rules. Kremlin critics say little has been done.
The Raspadskaya mine has reserves of some 450 million tonnes of coal and produced 8.9 million tonnes in 2007, according to company officials. Its owner Raspadskaya is 40 percent owned by steel-and-mining firm Evraz Group
Citigroup analysts said in a research note that "depending on how long the mine is be off-line, supply of coking coal in Russia will be limited". They said Raspadskaya produced 13 to 14 percent of total Russian coking coal concentrate output in 2009.
The mine supplies coking coal to Russian steel giants Evraz, MMK and NLMK, Citigroup said.
"The accident is bad news for Raspadskaya Coal and steelmakers alike," analysts at investment bank Troika Dialog said in a research note, with Evraz and Novolipetsk steel "likely to be impacted the most."
It said the mine could be out of operation for a month or two and is unlikely to reach full capacity until the fourth quarter of 2010. (Additional reportingby Tatyana Ustinova; Writing by Steve Gutterman and Dmitry Solovyov; Editing by Matthew Jones)