TBILISI (AFP) - Up to 20 people are still missing after devastating floods killed at least a dozen people in the Georgian capital Tbilisi, with escaped zoo animals - including two tigers - still on the loose on Monday.

The government of the former Soviet republic said the death toll after the Vere river burst its banks on Sunday following hours of torrential rain stood at 12 on Monday morning. Twenty people were missing as of Monday afternoon, Prime Minister Irakli Garibashvili's spokesman Manana Tokmajishvili told AFP, with the death toll expected to rise following Georgia's worst flood in decades. As many as 300 zoo animals also perished.

The torrents ravaged a zoo in the Georgian capital, with many animals including penguins drowning in the muddy waters. Other animals such as lions, tigers and even a hippopotamus escaped and were either recaptured or shot dead by police.

The hunt was still going on for the animals on Monday, Tbilisi zoo spokesman Mzia Sharashidze told journalists. "The search for animals is still underway," she said, adding that some 300 animals had died.

Some animals, including two bear cubs, were found kilometres away from the zoo and returned to their enclosures on Monday.

Ms Ivane Daraselia, the Tbilisi zoo's vet, told local television that two tigers, a bear, and a jackal were still on the loose as of Monday evening.

Survivor Bela Gvelesiani, whose house was destroyed by the flood, told AFP that "everything happened in just two minutes".

"I looked through the window and saw that the river was in my courtyard. I can't remember how we managed to get out. At first the water reached our ankles and in a split second we were up to our necks."

Her elderly neighbour Dusia Tsiklauri added: "My house was completely destroyed, but my thoughts are with my neighbours who died, with those still missing."

Another resident Aleko Korkotashvili said, "I saw a man clutching at a lamp pole in the middle of a violent torrent. He was screaming, asking for help, but we were unable to help him."

In an emotional show of solidarity after the disaster, hundreds of Tbilisi residents volunteered to join a clean-up operation across the city.

"What happened was an apocalypse," renowned Georgian actor Giorgi Nakashidze said as he helped National Guard soldiers clear mud and fallen trees from the streets.

"In my lifetime, I didn't see such a tragedy in our country. All those who care about our city, about people, should help rescuers and those who have suffered," he said in televised remarks.

"It was a disaster on an unprecedented scale," said 23-year-old volunteer Tsotne Japaridze.

The disaster left dozens of families without homes, wiped out several roads in central Tbilisi and seriously disrupted traffic.

Some homes were swept away along with cars by the torrents, with the floods even washing coffins out of the ground in the city cemetery.

Scores of Tbilisi residents volunteered to join a clean-up operation that could take weeks, Mayor David Narmania said.

Georgian Prime Minister Garibashvili praised the "tremendous" contribution of the volunteers.

"In our own country, we were moved by an unprecedented show of solidarity as volunteers took to the streets to help with the relief effort," he said in a written statement.

"The solidarity and support which Georgia has received in response to this disaster has been overwhelming." Local residents were also raising money and collecting food and clothes to help the victims.

Initially put at 13.3 million euros (S$20 million), the damage to Tbilisi's infrastructure would "in fact be much higher", Finance Minister Nodar Khaduri told journalists, adding that officials were still counting the costs.

Tbilisi Mayor David Narmania said reopening a 4km highway linking the city's two central districts would "take a long time".