Thousands of Brisbane residents were stockpiling food and stacking sandbags or fleeing their homes yesterday as the worst floodwaters to hit Queensland for 50 years surged towards Australia's third-largest city.

Many people in the state capital, fearful of the damage already done, appeared to have heeded the authorities' evacuation warnings. By last night, Brisbane's city centre was a ghost town populated only by a few shop owners hoping to save their businesses with last-minute barricades of sandbags and plastic sheeting.

Ten people died on Monday as cars and pedestrians were swept away in an "inland instant tsunami" that sent a wall of water coursing through the city of Toowoomba, west of Brisbane. More than 40 people were pulled from rooftops by military helicopters that were still searching for 90 missing people yesterday. Another 200 Australian Defence Force personnel are being dispatched to southern Queensland, which has been declared a disaster area. The flooding has claimed 14 lives in the last two weeks, but police fear the death toll could rise significantly as the bodies of people who may have drowned in their cars and homes are found.

"I think we're all going to be shocked by what they find in these towns that were hit by that tsunami," warned Queensland's state Premier Anna Bligh, as rescue crews took advantage of rare sunshine yesterday to search townships west of Brisbane.

From Toowoomba, 600 metres above sea level, the water flowed down the Lockyer valley and is heading towards Brisbane. The Brisbane river, which runs through the city – home to two million people – has already broken its banks in some areas, and residents of low-lying neighbourhoods have been leaving home.

Authorities have revised their figures up of the houses expected to be affected in Brisbane to 19,700. Electricity to some parts of the city has already been cut.

Queensland has been in the grip of floods – blamed on a La Niña weather pattern in the Pacific – for several weeks, and an area the size of France and Germany combined has been affected.

Bligh has said that people in Brisbane and the surrounding areas were "facing their greatest threat in more than 30 years" – a reference to the 1974 flood, which caused widespread damage.

In terms of economic impact alone, one central bank board member predicted the disaster could cost as much as 1% of Queensland's growth.

"We are now in a very frightening experience," she said yesterday. "Can I appeal to everybody that, at times like this, we need to all make an effort to stay calm, to be patient and to stick together." Bligh urged people to check on family and friends and offer shelter to those forced from their homes.

Arriving in Brisbane yesterday, Australia's prime minister, Julia Gillard, said she was deeply concerned about jobs and livelihoods.

"I have been shocked. I think we've all been shocked by the images of that wall of water just wreaking such devastation. The dimensions of it are truly mind-boggling," she said.

With around 1,500 people sheltering in evacuation centres in Brisbane and neighbouring Ipswich, and water released from dams added to the surge, the city's mayor, Campbell Newman, said the situation had "obviously demonstrably deteriorated" and warned that worse was to come. "Today is very significant, tomorrow is bad, and Thursday is going to be devastating for the residents and businesses affected," he said.

As constant rain pushed river levels still higher and water crept up to the steps of the Queensland state library, workers in the centre of Brisbane abandoned their high-rise offices, while shoppers mobbed a supermarket in the west of the city that had long sold out of bread and vegetables. At a nearby Sunshine Coast zoo founded by the late television star Steve Irwin, staff were tying up crocodiles in case they escaped in the deluge.

Last night, a steady stream of people arrived at the evacuation centre in Brisbane's showground, only a few minutes' drive from the swollen river. "I've lived in Brisbane for 18 years and I've never seen anything like this," said Chris Moxam, 24, from New Farm, one of the areas emergency services have listed as at risk of flooding. "I evacuated after I saw the TV pictures of what happened in Toowoomba. Everywhere in my suburb is at risk."

Although more than 80 people had registered at the evacuation centre, a huge, warehouse-like complex that can house 1,000 people, the Red Cross said it was expecting more arrivals. "We've got people coming from all parts of the city," Julie Groome, a co-ordinator for the organisation, said. Among residents who arrived at the showground were holidaymakers and homeless people with nowhere left to go. The centre has showers and toilets, a children's play area and even a place to accommodate pets.

The Salvation Army is helping with catering, and there are chaplains on duty, as well as St John Ambulance workers, to help the new arrivals.

Vicki Cella, who lives in Brisbane and is at the centre as a counsellor for a community group, tried to sum up the mood in Brisbane as rain pounded on the tin roof and evacuees bedded down on blow-up mattresses. "There's a level of disbelief at the moment. It feels surreal," she said. "We feel like we're in a movie. We know we don't know the full extent of it yet, but it's like a bad dream."