Across Asia-Pacific, a two-year-old slowdown in M&A continued into 2017, despite a strong final quarter.

Deal value totalled approximately $1.02trn across the region – not including Japan – in 2017, down 1.6% from 2016, according to a report released by Thomson Reuters.

But according to another report released by Mergermarket, total M&A volume in 2017 for the region was $673.5bn – up 2% from $658.8bn in 2016. Due to different methodologies, deal roundup statistics often vary from organisation to organisation.

Clifford Chance (CC) was the top-ranked Asia-Pacific M&A adviser by both Thomson Reuters and Bloomberg, which recorded the magic circle firm advising on $88.7bn and $86.9bn worth of deals respectively. Skadden Arps Slate Meagher & Flom and Herbert Smith Freehills claimed second and third place on both lists.

King & Wood Mallesons (KWM) retained the top spot on Mergermarket's list after advising on Asia-Pacific deals with a total value of $81bn – a 50% fall on 2016. CC and Skadden rounded out the top three.

Paris-headquartered commercial real estate company Unibail-Rodamco's $25bn acquisition of Australian shopping mall operator Westfield Corp was one of the top deals in the region. CC is advising Unibail-Rodamco alongside Shearman & Sterling, while Skadden and KWM are acting for Westfield with Debevoise & Plimpton.

CC and Skadden also advised some of the largest M&A deals in Asia. Skadden acted as regulatory counsel to a Chinese private equity consortium on its $16bn acquisition of Singapore-based warehouse operator Global Logistic Properties, while CC represented Bank of China Group Investment, a consortium member.

In October, both firms landed lead roles on a $5bn energy deal when CC advised US investment fund Global Infrastructure Partners on its acquisition of Singaporean renewable energy producer Equis Energy.

One driver for Asia's overall decrease in deal volume is a sharp fall of Chinese outbound deals compared to 2016. Thomson Reuters' data valued 862 outbound deals from China in 2017 at $141.5bn, down 35% from the year before.

In its report, Mergermarket attributed the fall to the Chinese Government's tightening control of capital outflow. "China is now urging companies to restrict overseas investments, or only to look outbound if business-critical, with companies having to stress the returns it will bring back to China to gain the green light from regulators," reads the report.

Mergermarket also noted political headwinds from the receiving end of Asia's outbound investments. "Multiple blocks by the Committee on Foreign Investment in the United States in 2017 have led would-be acquirers in China to rethink their strategies in the US," the report states. The research organisation found an 81% drop in the total value of US-bound Chinese investments in 2017, compared to a year earlier.

"Unhappy with being labelled national security risks, dealmakers have begun to consider avoiding US deals," Mergermarket observed, "with the potential for tech investments to be especially vulnerable to such shifts and with Chinese companies now starting to look for targets elsewhere."

Morrison & Foerster (MoFo), which has one of the largest Japan practices among US firms, unsurprisingly topped all three league tables for Japan M&A. In September, MoFo advised Toshiba on an $18bn sale of its chipmaking unit to a Bain Capital-led consortium in the largest M&A deal in Japan and the largest private equity deal in Asia last year.

Traditionally strong Japanese outbound volume dropped by 36.7% in 2017 from a year earlier, according to Mergermarket, while inbound investments – those going into Japan, especially those from the US – hit their highest volume since 2008.