Dutch defence minister Ank Bijleveld and his Belgian counterpart Steven Vandeput, in Brussels for a NATO meeting, signed a memorandum of understanding to begin the purchase procedure, the Belga news agency said, citing Vandeput.

The agreement calls for four frigates, which would built in the Netherlands, and 12 mine hunters, with 16 ships to be split evenly between the two sides.

Bids have been requested from Dutch builder DSNS (Damen Schelde Naval Shipbuilding) and the Dutch affiliate of French group Thales, the Dutch ANP news agency reported.

For Belgium, "some candidates have already been chosen... The goal is to make a decision by the end of the year," Laurence Mortier, a spokesman for the Belgian minister, told AFP.

The new ships should be delivered starting in 2023, the Belgian navy said.

The neighbouring countries' navies have collaborated for more than half a century and they cooperate closely in defence matters.