The new salvage ships with latest technologies and automated systems will be able to lift 400 tonnes each and detect sunken vessels, sources said.

The cost of the two ships will be no less than Tk 143 crore, and the government is willing to buy those through a long-term easy loan, they added.

They said the government is corresponding with the South Korean government and also trying to make an umbrella treaty with them.

Hamza, which was bought in 1964, cannot lift more than 60 tonnes. A rescue ship usually expires after 20 years, and Hamza passed its expiry date in 1984.

But authorities still keep it in operation due to a rise in launch disasters.

Comparatively new, Rustam was bought in 1984 and is also unable to meet the demand of the rescuers.

"Most of the ships now weigh 500 tonnes on an average. That's why those decades-old ships can't lift up any heavy vessels," said Md Rafiq Alam, director (planning) of Bangladesh Inland Water Transport Authority (BIWTA).

Rustam and Hamza were effective as long as wooden light vessels plied the rivers, he added. "It's now impossible to lift up a sunken ferry by them."

"The government has a plan to make an umbrella treaty with the Korean government. If signed, we may buy the ships under the treaty," said Alam.

The average speed of Hamza and Rustam is around six kilometres per hour that delays the ships in reaching the spot.

"Sometimes they reach the spot 48 hours after an accident takes place," said a BIWTA official.

Currently, Rustam is trying to lift the twin-decker MV Raipura, which sank with over 200 passengers aboard on Tuesday afternoon.

But its rescue wire is snapping again and again due to the strong currents and heavy load.