If confirmed, the result should mean Latvia remains a leading voice alongside its Baltic neighbours Lithuania and Estonia in pushing the European Union for a decisive stance against Russia.
But it could widen a rift between the country's Latvian majority and its Russian-speaking minority over their place in society amid widespread national anger over Moscow's actions in Ukraine.
The first Latvian head of government to serve through a full four-year term, Karins, a 57-year-old dual US and Latvian citizen, has benefited from his Moscow policy, which included restricting the entry of Russian citizens travelling from Russia and Belarus.
"We have known Russia's politics for years, we had been trying to warn our neighbours for years before the war started," Karins told reporters on Saturday after exit polls were published.
"We will continue to invest in our own defence ... to ensure that Latvia and the Baltic region remains as secure in the future as it is today."
An LETA/LSM exit poll showed New Unity at 22.5 per cent, twice the number of votes as nearest competitor, the United List of smaller parties.
The Greens and Farmers Union, a coalition of conservative groups closely knit around Aivars Lembergs, the long-term mayor of Ventspils who was put on a US sanctions list for alleged corruption in 2019, was in third place with 10.9 per cent.
Exit polls showed falling support for parties popular with Latvia's Russian-speaking minority, which makes up about a quarter of the country's population of 1.9 million.
The left-leaning Harmony party saw its support decline to single digits, with observers saying this was driven in part by ethnic Latvian voters turning away. Some Russian speakers were also disappointed by the party leadership criticising the Kremlin over Ukraine.
