Speaking to BBC Breakfast, Mr Killens said there were delays at urgent and emergency care departments which prevented ambulance staff handing over patients.
He said that one of the reasons for the pressure on the health system was down to winter viruses such as flu and Covid along with other factors.
“The pressure across the urgent and emergency care in the NHS is well documented. It’s a challenge here in Wales as it is in the rest of the UK,” he said.
Mr Killens said other factors had also contributed to the pressures placed on the system.
“It’s caused by many factors some associated with patients that are medically fit for discharge being unable to get back in to the communities because of the pressure in adult social care,” he said.
However, he added that while the pressure had continued overnight, the number of ambulances waiting were slightly less.
“As we go through this morning and we see the numbers of calls coming into us rising throughout the day as we normally would, we will see that similar situation of pressure arise today,” he said.
