need to run 300k updates in large sql script

I have a script that has around 300k update statements against a table with 500k rows. It seems to be taking about 1 second per update statement. So it might take 80 hours to run, 300k/60/60=83.3. I attempted to speed it up by putting around 10k rows within begin/end; and run as anonymous pl/sql block but it doesn't seem to be running any faster. Any ideas on how I might speed this up? This is an 18.14.0.0.0 database running on Solaris. I'm running sqlplus locally on the db server to avoid the network round