Chinese soccer clubs spent over $450 million on international transfers last year, around 2-1/2 times more than the year before, according to a FIFA subsidiary report released on Friday.

The spending spree, which has seen a series of big-money moves involving high profile players such as Chelsea and Brazil attacking midfielder Oscar and Argentina's Carlos Tevez, has raised eyebrows around the world and created unease.

It has also led to fierce criticism from officials and local media, prompting China to tighten rules over the number of overseas players able to appear in domestic games.

The report by Transfer Matching System (TMS) said Chinese clubs signed 159 players in international transfers in 2016.

The total of $451.3 million spent compared to $168.3 million in 2015 and was a seven-fold increase on 2013, the report said. It was also around 344 percent more than the rest of Asia combined, it said.

China is now fifth in terms of spending on international transfers behind England, Germany, Spain and Italy and has moved ahead of France, Portugal and Russia, the report added.

"The rapid nature of this growth is unprecedented," it said adding that the spending was "almost exclusively" on players coming from European clubs.

Overall, the report said that a total of $4.79 billion was spent on international transfers around the world last year, an increase of 14.3 percent over the year before.

The number of international transfers completed was 14,591, compared to 13,601 in 2015.

English clubs splashed out $1.37 billion, more than twice the next big spenders Germany with $576.4 million.

At the other extreme, clubs from the Oceania region signed only eight players from abroad between them, none of which involved a transfer fee.

TMS said that despite the figures, 85.6 percent of all transfers did not involve a transfer fee and only 1.5 percent involved a fee above $5 million. Transfers between clubs in the same countries were not included in the figures.