COLOMBO: Sri Lanka's parliament on Thursday voted to give President Gotabaya Rajapaksa widespread powers to appoint top officials and dissolve the legislature after an acrimonious two-day debate during which the opposition accused him of becoming a constitutional "dictator".

The populist leader was elected president in November and swiftly appointed his brother, former president Mahinda Rajapaksa, as prime minister. Gotabaya was a key defence official when his brother was president in the decade to 2015.

One member of the ruling SLPP party broke ranks undermining the two-thirds necessary to pass the bill, but eight opposition defectors saw the legislation through.

The government, which gets political and diplomatic support from China, has said the bill seeks to strengthen Rajapaksa to implement a manifesto promising "strong leadership."

However Justice minister Ali Sabry told parliament that some provisions granting greater immunity to Rajapaksa and removing financial oversight of state institutions were rolled back after a public outcry.

The president can now sack any minister, including the prime minister, and dissolve parliament after 2.5 years of its five-year term. Under reforms introduced in 2015, the president was not allowed to hold cabinet portfolios and could sack the 225-member legislature only after 4.5 years.