The Bank of Thailand has revised down its 2015 economic growth forecast to 2.7% from 3% after foreseeing a 5% export contraction from -1.5% earlier.
The gross domestic product forecast for 2016 was also trimmed to 4.1% from 3.7%, mainly due to external factors, assistant governor Mathee Supapongse said on Friday
The lacklustre export projection came after an economic slump in China and Thailand's other trading partners in the wake of declining farm and oil prices.
"The Thai economy may expand less than projected and we will review the situation at the meeting in December," he said.
The economy should expand at a faster pace in the latter half of this year than in the first six months, he added.
The government's economic stimulus measures would boost GDP growth by 0.1% while the impacts from the packages aimed at helping small and medium-sized enterprises would be felt next year.
Also on Friday, the Asian Development Bank (ADB) cut its 2015 GDP growth forecast to 2.7% from 3%, blaming weak domestic demand and the economic slowdown in China and other Asian economies.
Luxmon Attapich, senior economist for the ADB's Thailand mission, said the 2.7% growth forecast did not factor in the government's stimulus measures, which she termed unlikely to drive full-year growth...
The ADB sees public investment and tourism as the main drivers for economic growth in 2016, the forecast for which has been lowered to 3.8% from 4.1%.
Downside risks to the Thai economy include the China slowdown, public spending delays and drought, Ms Luxmon said.