Vietnam has accused a Chinese vessel of firing on a Vietnamese fishing boat in the disputed South China Sea and setting its cabin alight, reigniting tensions in the region over competing claims to the gas-rich waters.

The government described the incident last Wednesday as "very serious" and lodged a formal complaint with the Chinese embassy in the capital, Hanoi.

The fishing boat was near the Paracel islands when it was chased and shot at by an unidentified Chinese vessel, the government statement said on Monday.

It demanded China punish those responsible and pay reparations to the fishermen whose boat was damaged. The government did not say if anyone was injured.

The Chinese foreign ministry said it had no immediate response to the accusation.

There have been other clashes in the waters, often related to claims of illegal fishing or violations of China's unilaterally imposed fishing moratoriums.

Vietnam and China each claim large parts of the South China Sea; the Philippines, Malaysia, Taiwan and Brunei claim other parts.

The countries have been in dispute for years, but the profile of the issue has been raised in recent years because of China's economic and military growth and subsequent American interest. The Paracels, which were occupied by China shortly before the end of the Vietnam war in 1975, is a particular flashpoint.

China incorporated the Paracels and most of its other South China Sea claims within the newly declared Sansha city-level administrative unit last year as way of raising the region's profile and increasing funds for infrastructure and economic development.

The country is also boosting its civilian fisheries and maritime surveillance patrols in the area. China's navy conducts missions in the South China Sea, although it has sought to keep military units out of the disputed zones to avoid elevating tensions.