In seasonally adjusted terms, the value of investor loans fell 9 per cent, or almost $1 billion, over the month,
Over the year, investor lending is down more than 14 per cent.
Owner-occupier interest also cooled, down 1.9 per cent over the month.
Overall the value of mortgages issued over the month fell 4.4 per cent.
The impact of tougher credit rules demanded by APRA and the fallout from the bank royal commission's study of lax lending standards by mortgage brokers are taking their toll.
While house prices have been falling for several months, the pace has picked up, with Sydney house prices down 1.2 per cent over the first three months of the year and Melbourne's market down 0.7 per cent.
Things turning ugly: JP Morgan
JP Morgan's Henry St John said things have started to turn ugly for housing finance.
"These developments in investor and high loan-to-income lending are likely unfolding on a faster schedule than APRA may have originally intended," Mr St John said.
"To this point, it is likely that the scrutiny the royal commission is placing on the lending practices of the mortgage-broker channel, upon which the major banks have historically relied on for new lending growth, is acting as an additional catalyst."
"The weakness in new owner-occupier lending was well-dispersed, with all states seeing declines in their annual rates of growth save for Queensland," he said.
Investor activity likely to stay weak
Investors' share of borrowing hit a five-year low of 34.1 per cent in March, while first home owners' share also edged down for the first time in months.
ANZ's Daniel Gradwell said there are few signs investor activity would bounce back any time soon.
"While this result predates APRA's recent decision to remove the 10 per cent 'speed limit' on investor borrowing, it is hard to see a re-acceleration in the investor segment with sentiment clearly subdued," Mr Gradwell said.
However Mr Gradwell said recent decisions by several banks to cut investor mortgage rates, could prevent another sharp drop in borrowing.
There are also worrying signs in the residential construction sector with the number of loans in the sector falling for the second consecutive month, which may point to the recent bounce in building approvals running out of puff.
Source: ABC News
Updated