Two high-speed ferries - including one involved in a collision off Tsing Yi - have had their speed restricted after the Marine Department said they failed to travel safely during thick fog on Monday. The department yesterday said it had revoked the speed-restriction-exemption permits of mainland catamaran Nan Hua, which collided with a barge on Monday, and double-deck catamaran New Ferry LXXXIII, operated by New World First Ferry on the Hong Kong-Macau route. This means the two vessels will be restricted to 40 knots in Hong Kong waters. The department also announced last night that it was tightening speed restrictions under foggy conditions to improve safety. Under the new measures, speed-exemption permits on all fast vessels will be revoked when visibility drops below 1 nautical mile, as it did on Monday. A department spokesman said: 'It is important that the [ship] masters observe the conditions stated in the speed-restriction-exemption permit granted to the vessels to ensure safety. If the masters violate these conditions, the Marine Department will withdraw the [permit] immediately.' The department has also demanded all high-speed craft install an automatic identification system to help it monitor movement. Ship masters will also be told to navigate at a safe speed before they leave the China Ferry Terminal and Macau Ferry Terminal in low visibility. The Nan Sha 38 collided with the 50-metre Zhong Hang 98 on February 17 near the scene of Monday's crash, injuring 104 people.