Cabinet may need more time to make a decision on whether to cut blood-alcohol limits for drivers, says Prime Minister John Key.

The Government has been looking at whether to reduce the limit for full licence holders from 80 milligrams of alcohol per 100 millilitres of blood to 50 milligrams, but making a decision has proved difficult.

There have for a long time been calls from road safety advocates to reduce the limit and Mr Key said Transport Minister Steven Joyce had had advice from his own officials that it should be cut, but there was yet to be a consensus.

He told TVNZ that last year 36,000 people were convicted with a blood-alcohol limit of over 80 milligrams, but there were few driving statistics involving levels between 50 and 80 milligrams.

"I'd like to understand a little better what is happening between (50 and 80)," he said.

Mr Key said some comparable countries had the lower limits while others were in line with New Zealand's current limit.

Cabinet had discussed the issue a couple of times already and it was possible the issue would be carried over from today's meeting to next week's one before any decisions were made.