Almost as many migrants have arrived in Spain so far this year as came to the country throughout 2016, according to the International Organization for Migration (IOM).
Three times as many migrants have arrived so far in 2017 as the amount who had arrived in the same period last year.
More than 8,000 migrants have arrived by sea in Spain, almost as many as the 11,713 who have landed in Greece.
Spain is still far behind Italy, which received 96,861 until 9 August, according IOM figures.
The IOM say 11,849 people have arrived in Spain so far this year, compared with 13,246 in all of last year.
Earlier this week, footage showed migrants arriving by dinghy on a beach in Cádiz, southwest Spain, to the surprise of beachgoers.
"We assume that some of the change is due to the fact that the route [to Spain] is considered a safe route up to the coast through Morocco," Joel Millman, a senior IOM spokesman, said.
"It's possible that Spain will outperform Greece this year," Mr Millman said. "If so, that's a big change."
However, overall numbers of migrants have fallen by almost 60% from the same period the previous year.
The charity Médecins Sans Frontières (MSF) says Spain's reception centres are already overloaded and can not respond to the needs of the thousands of new arrivals.