Rats have infested a block of luxury flats - making nests in the walls and sparking fears over public health.

Residents of the Argus Lofts in Robert Street, in the North Laine area of Brighton, have complained of seeing and hearing the animals scurrying around inside the walls.

Pest controllers have been called in and were investigating the extent of the problem on Friday.

The problem only came to light gradually after thousands of polystyrene balls started to appear in the roads around the building in the past few weeks.

Residents and shopkeepers were baffled and put them down to someone playing a practical joke.

Residents' association secretary Adrian Stubbs said: "No-one could work out where it was coming from until we found out last night there were rats around the building."

Another resident, who asked not to be named, said the problem had started in a communal bin area.

He said: "The rats have obviously gone in there looking for food and have managed to burrow into the walls."

He explained that the walls were made of blocks with polystyrene in the centre and some around the bin area had nothing to cover them at the bottom.

He said: "The rats have got in and have been burrowing their way around. You can hear them. That's why the polystyrene has come out."

The Argus Lofts, which once housed the offices of The Argus, is a complex of shops, offices, affordable homes and luxury apartments. A two bedroom apartment was recently on the market for almost £400,000.

Steve Robinson, an assistant at New Heights furniture shop in the block, said: "The polystyrene has been annoying us for weeks. It blows in through the door and we have to hoover twice a day."

A spokeswoman for Brighton and Hove City Council said its pest control team had been carrying out treatment at the building yesterday and had given advice to the owners about measures to prevent further problems.

Agents Austin Rees, who manage the private flats, said it was aware of the situation and would be investigating further this week.

A spokeswoman for Hyde Housing Association, responsible for the affordable homes, said: "We are aware of a report from a resident about mice at this property and are working with the building's managing agents to investigate and resolve any problems as quickly as possible."