Analysts polled by Reuters had forecast a drop of 6.85%, worsening from February's 4.47% decline as the coronavirus pandemic weighed more heavily on global economic activity and demand.
"If export figures continue like this, they may not fall 8% or 10% this year... they may show close to zero growth, or a little more than that," ministry official Pimchanok Vonkorpon told a briefing.
The central bank has predicted exports, a key growth driver, will contract 8.8% this year.
March's exports were lifted by a 215% surge in gold shipments. Excluding gold, exports rose just 0.17%.
Exports to the United States jumped nearly 43% in March from a year earlier due to higher shipments of electronics and weapons after military drills. But shipments to China fell 4.8%.
While the pandemic has disrupted some trade logistics, demand for food products has increased, the ministry said.
China?s recovery from the outbreak and a weaker baht should also support Thai shipments, it added.
Imports in March rose 7.25% from a year earlier, led by fuel and raw and semi-finished products. That compared with the forecast 10.79% drop, and February's 4.3% decline.
March's trade surplus was $1.59 billion versus a forecast for a $2.9 billion surplus and February's $3.9 billion surplus.
By Orathai Sriring and Kitiphong Thaichareon