After an all-night search, an adolescent boy was found on Wednesday morning, followed a few hours later by a second, officials in the resort town of Bad Reichenhall in the German Alps said.

A woman and a young girl who were trapped inside the vast pile of concrete and metal, were believed to be dead, Hubertus Andrae, the police chief of the nearby town of Traunstein, said.

"There is no sign of life," Andrae told a press conference.

He said rescuers had been painstakingly searching for the two with the help of sniffer dogs.

"It is a difficult, slow search. Every time the men searching have to try and establish whether the dogs have identified the right spot."

Rudi Zeif, the fire services chief in Bad Reichenhall, vowed that the search, which involves some 200 rescue workers, would go on until the last of the missing had been recovered.

Of the 13 people found dead since the roof of the ice skating rink collapsed amid heavy snow on Monday, 11 were children or adolescents. The other two victims were women of around 40.

All those found so far are from the region, and as darkness fell Tuesday in the town of 18,000, several hundred people gathered in front of the town hall for a candlelit vigil for the dead.

According to local radio, a funeral ceremony would be held next Tuesday.

Thirty-four people were injured when the roof collapsed some 15 minutes before the rink was due to close for the day. Thirteen of them were still in hospital but their lives were not in danger, according to German radio.

Chancellor Angela Merkel on Tuesday expressed her condolences to grieving families and said the federal government would do everything in its power to help the Bavarian state authorities cope with the disaster.

"I, and all of us, have been particularly moved by the cruel fate suffered above all by children and adolescents who wanted to spend a carefree holiday with their family members," she said.

"We are mourning with the loved ones and our thoughts are with those who lost friends."

It was not immediately clear what caused the flat roof of the building to cave in, in a region accustomed to heavy snowfall.

Der Tagesspiegel newspaper on Wednesday cited weather services as saying there must have been about 180 tonnes of snow on the roof when it collapsed.

The coach of a local ice hockey club, Thomas Rumpeltes, said the snow was due to have been cleared from the roof before the accident.

Rumpeltes said authorities told him of the impending clearance shortly before the accident and he cancelled a practice at the rink for a youth team.

He said no one had warned of any risk of the roof being unstable and that the snow removal was a precautionary measure.

Mayor Wolfgang Heitmeier has dismissed accusations of negligence for allowing the rink to remain open, saying the roof had been examined in the late morning Monday to determine whether it could withstand the weight of the snow.

He rejected speculation that the authorities knew of structural problems, saying he "could not explain" what caused the collapse.

State prosecutor Helmut Vordermayer has said evidence was being collected and a probe into the accident had been opened.

A member of the board of the German Alliance of Cities and Towns said calls for stronger safety measures were not appropriate this time as "we first need to determine the causes" of the accident.

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