China is expected to build 8500 km of metro systems in 2020, giving it the world's longest underground railway network, the government said Friday.

Nineteen cities have recently expanded their subway systems, with the total mileage expected to hit 3000 km at the end of the year, Chinese Minister of Transport, Yang Chuantang, was quoted by the China State Journal.

The public transport, especially the metro, has had a significant effect on relieving congestion in Beijing, and the government will inject more funds to promote their development, Dai Junliang, vice mayor of Beijing, said.

Four new subway lines were opened to the public this month that the capital's subway will extend to 527 km, the longest in the country.

Daily passengers will gradually increase to more than 10 million, the Beijing Transportation Commission, said.

To ensure safety with such a large number of passengers, safety should be strengthened, Yang said.

Number of staff in some metro systems are not sufficient, and some staff are not trained in the use of high technology, leaving the possibility of security risks, he said.

On Thursday, the Beijing subway system held a mock subway derailment handle.

The teams of bus and metro, medical personnel and traffic police, tested rescue trapped passengers and resume passenger service.

Chen Wen, director in charge of emergency response and coordination with the Group of Beijing subway, said more than 70 emergency plans have been prepared for different situations.

Beijing has 26 professional rescuers emergency with over 500 members and has over 600 exercises each year to hone the skills to deal with emergencies such as a fire in a subway station or equipment failures .

In addition to regular exercise, Mr. Yang called for laws and regulations to promote improved management and security meter.