BANGKOK (AP) ― Soldiers, civil servants and families worked frantically Tuesday to add more than 1 million sandbags to Bangkok’s vulnerable northern flood defenses after the city’s governor warned they were needed to keep waters from swamping the capital.

Gov. Sukhumbhand Paribatra said late Monday that a 6-kilometer flood wall on the edge of the city’s suburbs was vulnerable from massive pools of runoff flowing down from the north, signaling the threat to the city was still grave. He said the wall needed to be reinforced by Wednesday night.

“Every second counts,” said Sukhumbhand Paribatra, whose call for city residents not to let down their guard contrasted government statements that the flood threat to Bangkok appeared to be easing.

At least 315 people have been killed in the worst flooding to hit Thailand in more than 50 years. Monsoon downpours that began in July have inundated two-thirds of the country, and some areas remain under more than 2 meters of water that is unlikely to dissipate for weeks.

The floods have brought life to a standstill in affected towns and cities. Economic analysts say the floods have already reduced GDP projections for 2011 to as low as 2.5 percent from 4.4 percent and could inflict around $6 billion in damage ― an amount that could double if floods swamp Bangkok.

Sukhumbhand said barriers had to be built up at several canals carrying overflow water from heavily inundated Pathum Thani province, just north of Bangkok, where soldiers have joined volunteers in trying to save the country’s oldest industrial estate from being inundated.

Sukhumbhand has consistently taken a more cautious view of the flooding threat than the government of Prime Minister Yingluck Shinawatra, who also heads a rival political party. Officials in charge of fighting the flood had suggested earlier Monday that Bangkok would be spared thanks to the city’s complex system of flood walls, canals, dikes and underground tunnels that help divert vast pools of runoff south into the Gulf of Thailand.

Outside the capital, thousands of people remain displaced and hungry residents were struggling to survive in half-submerged towns. The military has been mobilized to help deliver relief supplies to stranded residents.

The potential economic costs were underlined in the effort Monday to save the Nava Nakorn industrial estate in Pathum Thani, Thailand’s oldest factory park.

Shortly after noon, the government’s Flood Relief Operation Center ordered all factories there to halt work and prepare their workers for evacuation after water started to break through makeshift barriers erected over the past few days.

Officials later said they managed to limit the flooding to under 10 percent of the estate, and had the situation under control.

At least four other major industrial parks have been inundated, leaving upward of 100,000 workers idle and disrupting supply chains, especially in the automotive and electronic industries.

The Labor Ministry said that more than 260,000 people had lost jobs and 6,533 businesses nationwide had to close due to floods in the period Oct. 10-12. Thailand’s Central Bank last week estimated that the total cost of the floods could be 100 billion baht ($3 billion).

The flood center’s spokesman, Wim Rungwattanajinda, said 200 buses and trucks were mobilized to take evacuated workers to emergency shelters, including a huge temple complex belonging to the Dhammakaya Buddhist sect that could house as many as 5,000.

Companies with operations at Nava Nakorn, which was established in 1971, include Japanese watchmakers Casio and Seiko, the Swiss powdered milk and food producer Nestle, Japanese electronics firm Toshiba and hard drive maker Western Digital, which has already lost another production facility at another industrial park.

The biggest blows were suffered by Honda and Toyota for whom Thailand is a major production base. Both have been forced to stop all work here due to flooding of their facilities.

Many of the factories in flooded industrial estates are producers of specialized components, such as parts for computer hard drives, producing a knock-on effect for manufacturers in other areas unaffected by flooding that are unable to source needed parts.

Last week, a Japanese trade organization criticized the Thai government for allegedly failing to provide timely and accurate information about the situation in the central province of Ayutthaya, where hundreds of factories have been devastated, including electronics makers and automotive parts suppliers.