Vietnam's immigration authorities are issuing separate visa sheets to new Chinese passport holders instead of stamping directly on visa pages, after Beijing issued new passports that  include a map of territories also claimed by other countries.

At the Lao Cai border gate in northern Vietnam bordering China, 111 new Chinese passports were proclaimed by Vietnam as invalid as of Sunday, but the holders were able to enter the country with the visa sheets, according to Vietnam's tuoitrenews.vn website. Meanwhile, Vietnam's government lodged a formal complaint with the Chinese embassy, according to Bloomberg.

The map lays clear claim of China to the maritime sovereignty in the South China seas. But Vietnam is refusing to accept this.

On Saturday, the Indian embassy in Beijing began stamping new Chinese passports with a map showing a border territory disputed by the two countries as claimed by India.

The Philippines also "strongly protests" China's decision to include the disputed maritime areas in the South China Sea in its passport map, according to Asian News International.

This May, China started issuing the new passport that contain an electronic chip, which includes the holder's fingerprints, signature and photographs.

The 48-page passport not only uses scenery as background for many pages, but also includes a map of China.

According to a previous Global Times report, the new chipped-passport is valid for 10 years, and over a million of them have been issued.

The episode does not change the fact that the disputed territories belong to China, nor does it mean that China plans to solve the disputes by issuing a new passport, scholars say.

"The on-going passport row can be solved via diplomatic channels.  After all, it is not possible to suspend Sino-foreign personnel exchanges due to this episode,"  Zhao Gancheng, an expert on Southeast Asia at the Shanghai Institute for International Studies, told the Global Times on Monday.

Since tensions over territorial disputes with neighboring countries in the South China Sea and East China Sea escalated in the past year, China has adopted a series of measures to strengthen its hold on these areas, besides increasing maritime patrols.

Sansha city was established in July, which will cover more than 2 million kilometers of sea waters in the South China Sea, including those bordering Vietnam.

In September, the State Oceanic Administration announced that unmanned planes will be used to enhance surveillance on the sea and islands, including the Diaoyu Islands in the east and other islands in the south.

Also in September, China filed a copy of the Diaoyu Islands baseline announcement to the United Nations.