China's Exxim Bank will fund the purchases with a lending agreement due to be signed between Colombo and Beijing shortly, officials said.
The railway official said the railways' rolling stock is in desperate need of modernisation.
"We last bought about 150 carriages from Romania in 1992," Wijesekera told AFP. It purchased 15 engines from China in 2000.
Delivery of the locomotives and coaches was expected to start in August.
Sri Lanka Railways was built in 1864 by the British to transport tea, coffee, rubber, cinnamon and other spices from the hilly interior to Colombo for export.
It moves 300,000 passengers daily on 324 trains between 320 stations across the island of 19.5 million people.
Over the years the railway, which employs 17,000 workers, has lost market share to road transport as a lack of investment has diminished its speed and reliability.The railway makes revenues of around three billion rupees (27.78 million dollars), but has not made a profit since 1943 and needs a state subsidy of seven billion rupees to survive, according to central bank figures.