If they were not evacuated immediately, "the situation will be more than dramatic tomorrow", he said.
Mr Oyarzun said the humanitarian concerns were not limited to the town of Madaya, which is situated in the southwest of the country near the Lebanese border.
"I think that you are all aware that we are talking about 400,000 people living under besieged areas in Syria.
"It's not only about Madaya, in Madaya we have 42,000 people. It's also about many other besieged areas by Daesh (Isis) and other groups that we have to take care of."
Mr van Bohemen also responded to claims from Syrian officials that there was no starvation in Madaya and the crisis had been fabricated by "hostile governments" and media.
He said there was "definitely a situation" in the township and this had been witnessed by the aid convoy when it arrived today.