Rescue workers with search dogs picked through rubble of an indoor water park Sunday, trying to find survivors of a roof collapse that killed at least 25 people and injured dozens more.

Prosecutors, meanwhile, suspect the cause was probably faulty construction or maintenance and opened a criminal investigation.

The concrete-and-steel roof collapsed Saturday evening at Transvaal Park on Moscow's southwestern outskirts - one of many leisure and entertainment facilities built in recent years to attract cash from residents of the Russian capital and its suburbs.

Initial reports said the roof collapsed after an explosion, but Moscow Mayor Yuri Luzhkov and other officials said there was no evidence a blast caused the disaster, which comes as many in the capital are still shaken by a deadly Feb. 6 subway bombing blamed on Chechen rebels.

Investigators were considering several theories of what caused the collapse, including a heavy buildup of snow, the difference between the indoor and outdoor temperatures, and the seepage of water into the concrete supports.

Moscow prosecutor Anatoly Zuyev said his office had opened a criminal investigation and suspects the cause was probably faulty construction or maintenance.

Zuyev said investigators began questioning managers of the park Sunday and would also question its architects and builders, as well as witnesses.

Rescue workers shoveled snow from a tangled mass of steel and concrete, while cranes lifted chunks of concrete, car-sized metal beams and other debris. The facade of park appeared intact.

Generators were used to pump heat into the area to aid any survivors trapped underneath the rubble. Rescuers periodically ordered silence to listen for signs of life.

By noon, authorities recovered 24 bodies and one victim died in a hospital, bringing the death toll to 25, the Interfax news agency quoted Moscow official Nikolai Kulikov as saying.

In televised comments, Emergency Situations Minister Sergei Shoigu said 17 people were believed missing, and rescue efforts were slated to continue through Sunday evening.

Ninety people were hospitalized, including 28 children, NTV television reported, adding that four people were in critical condition and 16 in serious condition.

A child's birthday party was being held in the pool area when the roof collapsed, said Moscow police spokesman Kirill Mazurin.

In all, there were about 800 people in the water park complex, and 352 of them were in the pool area when the roof collapsed about 7:30 p.m. as visitors basked in the balmy indoor area while temperatures outside hovered around 5 degrees.

Roman Yazymin, 29, was sun-tanning in a solarium on the upper floors of the complex when he heard a loud noise and the crash of shattering glass.

"It wasn't an explosion, but the noise of metal collapsing," he said and noted that as he walked through the complex to retrieve his clothing "everything was in blood."

Rescue workers rushed bloodied, moaning people clad in bikinis and swim trunks on stretchers to waiting ambulances, while those who could clambered out barefoot into the snow.

The complex, which opened in 2002, was designed by a Russian architectural firm and built by a Turkish firm, Kocak, Ekho Moskvy radio said. It included a large pool, an artificial river and a water slide.