The government's economic planning unit feels more upbeat about prospects, maintaining its growth forecast at 3.5% to 4.5% for this year.
But the research house of the University of the Thai Chamber of Commerce (UTCC) is taking a bleaker perspective, now predicting Thai economic growth could come in at less than 3%.
The National Economic and Social Development Board (NESDB) on Thursday reported to the weekly economic ministers' meeting chaired by Prime Minister Prayut Chan-o-cha that first-quarter growth could come in at 3%.
Growing tourism, recovering private consumption, private investment and accelerated government spending would be the drivers.
NESDB secretary-general Arkhom Termpittayapaisith said 55% of this fiscal year's 60-billion-baht budget slated for road construction by the Highways Department would be disbursed by next month.
Bids are expected to be called in the second or third quarter for investment in the first phase of six 900-kilometre double-track railways worth a combined 117 billion baht.
Mr Arkhom said private investment through promoted projects by the Board of Investment (BoI) and factories that won operating licences from the Industry Ministry had also shown progress in construction. In the first three months of this year, some 700 projects worth a combined 110 billion baht won BoI approval.
Household consumption in the first quarter is projected to show 1-2% growth, a relatively slow rate due to low commodity prices from drought in many areas of the country.
Mr Arkhom said tourism, which accounts for 10% of GDP, would be a major contributor to the economy this year.
He cited a report by the Tourism and Sports Ministry showing a 26% increase in international tourist arrivals year-to-date as of Wednesday, generating 300 billion baht in revenue.
Revenue collection in the first five months of fiscal 2015 grew by 0.9% year-on-year, with the figure increasing by 1.1% for January and February alone.
Value-added tax collection rose by 0.5% in the first two months.
However, exports contracted by 4% in the first two months, with shipments down to all of Thailand's major markets except the US.
Despite the poor performance of the first two months, the NESDB is maintaining its export forecast at 3.5% growth for the full year.
In a separate development, UTCC yesterday cut its economic growth forecast to only 3.2% this year from between 3.5% and 4% forecast last November due mainly to delayed budget disbursement, falling farm prices and the slower-than-expected global economic recovery.
It also expects the economy will grow by only 2.2% in the first quarter.
"We foresee the Thai economy still has room to grow this year, possibly by less than 3%, given the myriad negative factors exerting pressure," said Thanavath Phonvichai, vice-president for research.
"Exports are expected to grow marginally by only 0.4% for the full year against a 4.1% expansion in the earlier projection, with inflation standing at 0.5% from 2.3%."
He said the Thai economic growth would be determined this year primarily by the global economic recovery and how quickly the government could stimulate the economy through stimulus measures and infrastructure investment.
Mr Thanavath also called on the government to speed up its measures to rein in the baht's appreciation and ensure its movement in line with the currencies of Thailand's competitors. The baht gained 0.2% against the US dollar in the first quarter, while other Asian currencies were 4-10% weaker on average.