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Authorities are investigating after 16 residents of the same apartment block reported suffering with headaches and nausea, with five taken to hospital.

About 60 residents of Bay Chambers, in the Butetown area of the capital, were evacuated on Thursday evening.

The source of the illness was initially suspected to be a carbon monoxide leak, but Public Health Wales said air quality tests had ruled that out.

Residents have been allowed to return, but have been advised not to drink tap water as a precaution while investigations continue.

Police, four ambulances and five fire appliances attended just after 22:00 BST.

One of the five people taken to hospital was kept in overnight for observations at the city's University Hospital of Wales.

Bottled water has been delivered to residents while the source of the illness is investigated.

Mark Bowditch, of South Wales Fire and Rescue Service, told ´óÏó´«Ã½ Radio Wales Breakfast a major incident was declared after officers responded to "a suspected carbon monoxide incident".

He said the residents were evacuated from the building to allow fire officers to carry out monitoring, but after nothing was found they were allowed back home.

"From a fire service point of view, we carry out significant monitoring, using various pieces of equipment which all gave a zero reading, so from our point of view we were more than happy for residents to go back into the building," said Mr Bowditch.

He said there would be further investigations "to understand what could have caused these individuals to feel unwell".

The evacuated residents were taken to a "rest centre" in the nearby Coal Exchange building.

The incident was declared over after six hours, and police said the investigation was ongoing.