BANGKOK (AP) — Seasonal monsoon rains may worsen flooding that has already badly affected about a third of Thailand, officials said Monday as flood gates and pumping stations were being used to mitigate the potential damage.

A tropical storm over the weekend swept through the upper part of the country, causing flash floods that affected 58,977 families, the Department of Disaster Prevention and Mitigation reported.

Boontham Lertsukekasem, the department’s director-general, told reporters that 12 provinces along the Chao Phraya river, including Bangkok and the old capital Ayutthaya, should be prepared for new flooding as water levels increase in the Chao Phraya dam by 30 centimeters to 1 meter (1-3 feet) over the next few days.

Soldiers helped fill sandbags in Ayutthaya.

In Bangkok, Gov. Aswin Kwanmuang declared on his Facebook page the situation in Bangkok was not yet critical but the city was carefully operating flood gates and pumping stations, among other preparations.

Sections of the northeastern province of Nakhon Ratchasima had severe flooding when a reservoir overflowed, forcing people to walk through knee-deep water and inundating the ground floors of many homes.

Prime Minister Prayuth Chan-ocha and several Cabinet members met with flood-affected people and handed out aid Sunday in Sukhothai province.

Thailand has a tropical climate and often sees flooding that causes millions of dollars in damage during its monsoon season from July to October.