MANILA, Philippines — While China sent its maritime militia in response to the Philippines' upgrade of its facilities on Pag-asa Island, Vietnam has also been expanding its facilities on its outposts in the Spratly chain in the South China Sea.

Washington-based think tank Asia Maritime Transparency Initiative reported that Hanoi has extended its runway on Spratly Island, its largest outpost and administrative center in the area.

Contrary to China's industrial-scale dredging on features in the Spratlys, Vietnam used construction equipment to dredge up the reef surrounding the island and covered it with sand.

The report noted that Vietnam's process was more time-consuming and less environmentally disastrous than what China did.

Hanoi's runway on Spratly Island has been extended to 1,300 meters from 750 meters, the AMTI reported.

"Since 2017, Hanoi has put the finishing touches on the ends of the airstrip. In the middle of that year, it completed two large sets of hangars at either end of the runway," the AMTI said.

The hangars on the Vietnam-controlled island are likely to host PZL M28B maritime aircraft and CASA C-295 transport planes in the future.

Vietnam also had communications facilities installed on the island, as well as new buildings topped with solar panels.

Aside from Spratly Island, Hanoi had upgraded its facilities on Pearson Reef with the construction of a helipad, solar panels and planting of vegetation on its new landfill.

The Southeast Asian country's facilities on surrounding reefs, such as Petly and South Reefs, have also been expanded with new structures since mid-2017.

"It seems that regardless of external factors, whether amid negotiations and relative calm or tensions and threats of violence, Hanoi is committed to a steady but modest expansion of its capabilities in and around the Spratly Islands," the report read.

While Vietnam does not engage in large-scale militarization of features like China, its upgrades on its feature lean toward monitoring areas in its control.

The AMTI noted that Hanoi's facilities do not include structures that could house attack aircraft.

"Instead, Hanoi’s upgrades seem geared toward expanding its ability to monitor and patrol contested waters and, especially in the case of its pillbox and DK1 platforms, improve living conditions and ensure it can resupply by air if necessary," the AMTI said.

Meanwhile in the Philippines, hundreds of Chinese vessels have been stationed in areas near Pag-asa Island and Kota Island in the West Philippine Sea.

The AMTI earlier reported that Chinese ships have been operating in the area around the same time that the Philippine started upgrading its runway on Pag-asa Island last year.

The military confirmed that they have been monitoring the presence of hundreds of Chinese vessels near Pag-asa Island, believed to be part of China's maritime militia.