TAIPEI, May 30 (Xinhua) -- Taiwan's manufacturing sector displayed improving signs in April after five straight months of contraction, but uncertainties still remained amid an escalating trade friction between the United States and the Chinese mainland, according to a leading economic think tank.

The monthly composite index for the manufacturing sector in April flashed a "yellow-blue light" that signals sluggishness, improving by 1.2 points from a month earlier to 10.72 points, according to the preliminary results of a survey by the Taiwan Institute of Economic Research (TIER) Thursday.

The barometer had been in the contraction field for five months since November last year.

Under TIER's five-color system to assess the sentiment of the manufacturing sector, a blue light (10.5 points and below) indicates contraction, yellow-blue light (10.5-13) means sluggishness, green light (13-16) signals stable growth, yellow-red (16-18.5) suggests fast growth, and red light (above 18.5) represents prosperity.

About 53.88 percent of the manufacturers covered by the think tank's monthly survey flashed a blue light for contraction in April, compared with 74.1 percent in March, while 24.03 percent flashed a yellow-blue light for sluggishness, up from 22.50 percent in March, and 19.98 percent flashed green light for stable growth.

Only 0.23 percent of the manufacturers flashed a red light for prosperity, and 1.88 percent for fast growth.