Melbourne, Jul 14 (IANS): Australian authorities on Friday asked residents to evacuate more than 100 homes in Melbourne as a huge fire is spreading hazardous smoke across the city, the media reported.

Four people have been taken to hospital and a further eight treated for asthma symptoms since the fire began at a recycling plant on Thursday, reports the BBC.

Described by authorities as "the size of a sports field", the fire is likely to burn for at least two more days.

It has cast smoke and ash as far as 15 km away.

Metropolitan Fire Brigade Commander Brendan Angwin said the blaze is being fuelled by thousands of tonnes of plastic, cardboard and paper.

"It is extremely difficult to gain access to the fire," he told the Australian Broadcasting Corporation (ABC).

"We are really concerned for firefighter safety."

The local Environmental Protection Agency has described air quality in the vicinity as "very poor", the BBC reported.

Authorities have urged anyone near the fire, at Coolaroo in Melbourne's north, to take shelter indoors.