Kannur, a politically sensitive northern district, recorded the highest turnout of 47.61 per cent.
Thiruvananthapuram saw the lowest of 36.14 per cent in the first six hours after the polling began at 7 AM, election officials said.
A total of 1,203 candidates are in the fray.
Polling was peaceful across the state so far, police said.
Tight security has been put in place with deployment of about 52,000 police personnel from state police forces.