SEOUL, Nov 26 (Reuters) - South Korea's transport ministry plans to meet with the striking truckers union on Monday for negotiations, a ministry official said on Saturday.

Thousands of unionised truckers on Thursday launched their second major strike in less than six months seeking better pay and working conditions. The action is already disrupting supply chains across the world's 10th largest economy, affecting automakers, cement and steel producers.

“We requested dialogue with the union and the truckers union replied that they would meet with us on Monday ... the talk is not yet finalised, but we plan to meet with the union and talk," the ministry official told Reuters.

"We are ready to talk about reasonable demands of the trucker union at any time and will put efforts to solve the issues," the ministry said in a statement on late Saturday.

A union official confirmed Monday's meeting, which would be the first official dialogue between the two sides.

The transport ministry said about 5,000 people attended the strike on Saturday in 136 locations nationwide, down from 9,600 people on the first day of the strike.

Container traffic at ports dropped to 19% of normal levels as of 5 p.m. (0800 GMT) on Saturday, the transport ministry said, down from 35% of normal levels in the morning.

South Korean President Yoon Suk-yeol warned on Thursday that the government would consider various options, such as issuing an order to break up the strike, calling it as an illegal and unacceptable move to take the national supply chain "hostage" during an economic crisis.

According to South Korean law, during a serious disruption to transportation the government may issue an order to force transport workers back to their jobs. Failure to comply is punishable by up to three years in jail, or a fine of up to 30 million won ($22,550).

The Korea International Trade Association (KITA) received 53 reports of disrupted logistics from 31 companies since the strike began.

The cement industry estimated an output loss of about 37 billion won ($27.73 million) as of Friday, said lobby group Korea Cement Association. It added that the industry only managed to ship about 20,000 tonnes of cement on Friday, just about 10% of usual daily shipments.