Police are investigating a killing at an asylum centre in Sweden after a fight broke out among residents.It is the second such incident in a month after a 22-year- old employee at a refugee centre for unaccompanied minors was stabbed to death, prompting concerns that authorities were being overwhelmed by the number of asylum seekers in the country.Police said the fight broke out on Saturday afternoon in Ljusne, a town of about 2,500 people on Sweden's east coast, some 240 km north of Stockholm, but gave no further details.Swedish media said four people had been involved and a sharp object had been used. It appeared to be a fight among people living at the centre and no staff were injured.Sweden reversed its open doors-policy on immigration late last year and has introduced border controls and identification checks to stem the flow of asylum seekers that reached a record 163,000 last year.The country's migration agency expects up to 140,000 asylum seekers in 2016 but the government has said it will not allow numbers to get anywhere near that, vowing to introduce further measures to curb the influx if needed.