Residents living in downtown Ratchaburi may soon be ordered to evacuate their homes as authorities prepare to defuse seven World War II-era unexploded bombs found on the bed of the Mae Klong River.

The bombs were first discovered by the State Railway of Thailand's workers who were working on the first phase of the double-track rail upgrade project between Nakhon Pathom and Chumphon.

Another bomb was found buried between Khao Tao and Wang Phong train stations in Prachuap Khiri Khan's Pran Buri district.

SRT acting governor Worawut Mala said there is a possibility more unexploded ordnance may be discovered as the project moves on to its second phase, which will see works carried out between Chumphon and Songkhla.

The SRT's acting governor added a blast could damage structures that lie within a two-kilometre radius, which include military camps, temples, markets, schools, the City Hall, as well as numerous homes.

Experts from Germany will be invited to assist because retrieving unexploded underwater ordnance requires a high degree of technical expertise, he said.

Various methods have been considered to safely dispose of the bombs, but the most suitable way is to defuse them underwater, he said.

The bombs were dropped during Allied air raids in Ratchaburi after Japanese soldiers invaded Thailand in 1941.