People watch as water from the Imjin river is discharged through the Gunnam Dam in Yeoncheon following heavy rain fall on Aug 6, 2020. (YONHAP / AFP)

SEOUL - A massive search was under way in the Republic of Korea (ROK) on Thursday for five rescue workers swept over a dam when their boats overturned in surging floodwaters, while President Moon Jae-in raised concerns about the Democratic People's Republic of Korea (DPRK) releasing excess water without notification.

Heavy rain has also fallen in the DPRK and state media published pictures of flooded streets but did not give any detail of damage or casualties

Parts of the ROK have seen 44 consecutive days of rain, the longest monsoon since 2013, and continued showers across the Korean peninsula are threatening to bring new floods and landslides.

In a visit to one of the hardest-hit areas, near the border with the DPRK, Moon expressed regret about a DPRK’s move earlier in the week to suddenly release excess water from a dam without notifying the ROK.

While no specific damage from the release was reported and it was unrelated to the rescue accident, Moon said the unexpected rush of water had made it more difficult for the ROK’s authorities to manage already swollen rivers.

Heavy rain has also fallen in the DPRK and state media published pictures of flooded streets but did not give any detail of damage or casualties.

The government in the DPRK had issued a flood alert for areas near some its biggest rivers and lakes, the Rodong Sinmun newspaper reported.

ROK’s Prime Minister Chung Sye-kyun, meanwhile, visited a river near the city of Chuncheon, to the northeast of Seoul, where more than 800 police and fire officials using seven helicopters and 69 boats were searching for the missing rescue workers.

ALSO READ: Flood-hit ROK guards against coronavirus at relief shelters

Two rescue boats were trying to free a police boat stuck in wire by a dam near Chuncheon when they overturned, Yonhap news agency reported.

One man was rescued at the scene but seven others were swept over the dam’s floodgates.

One of the seven, a 68-year-old man, was found near the dam suffering from cardiac arrest but was recovering. Another, also 68, was recovered dead about 20 km downstream, Yonhap reported.

A local police official could not confirm the details.

Elsewhere in the ROK, at least 16 people have been killed and 11 are missing, with more than 1,600 people displaced over recent days.

READ MORE: Heavy rains in ROK displace more than 1,000 people, 14 dead

In Seoul, the Han River swelled over its banks in some areas after authorities were forced to open floodgates on upstream dams. Some highways by the river had to be closed, Yonhap reported.