Most Southeast Asian markets wavered between small gains and losses on Monday, as lingering concerns about the coronavirus pandemic outweighed a landmark output cut by OPEC+, while the Philippines rose on hopes of monetary easing.

OPEC and allies led by Russia agreed on Sunday to a record cut in output to prop up oil prices, though global demand concerns remained amid large-scale virus-related lockdowns around the world.

However, the oil output cut of about 9.7 million barrels per day (bpd) was below expectations of a 20 million bpd cut, according to Suria Dharma, Head of Equity Research at Samuel Sekuritas Indonesia.

"People are still concerned with COVID-19, which has not been slowing down," Dharma said. Indonesia on Monday announced 316 new cases of the coronavirus, while Malaysia reported 284 fresh infections.

Indonesian stocks closed down 0.5%, with financials the top drag on the index. PT Bank Central Asia Tbk shed 1.3%. On the upside, the Philippine index climbed 1.8%, with conglomerates Ayala Land and Ayala Corp gaining 4.5% and 2% respectively.

Monday's gains could be attributed to investors' favourable perception of local COVID-19 containment measures in the Philippines, as well as expectations of further monetary easing, according to Ruben Carlo O. Asuncion, chief economist at the Union Bank of the Philippines.

The Philippines' central bank governor had said on Sunday that another 200 basis point cut in the bank's reserve requirement ratio is "forthcoming" and signalled more cuts in its policy interest rate.

Vietnamese equities ended up 1%, with financials the top gainers. Thai shares see-sawed throughout the day and closed 0.7% higher, helped by gains in the real estate sector. Central Pattana Pcl rose 2%. Shares in Singapore and Malaysia were little changed throughout the session.