* Philippines to build port and upgrade airstrip
* Trips to disputed zone cancelled over worry about China
* Duterte to meet Chinese vice-premier on Friday (Writes through with defence minister's comments)
MANILA, March 17 (Reuters) - The Philippines said on Friday it would strengthen its military facilities on islands and shoals in the disputed South China Sea and announced initial plans to build a new port and pave an existing rough airstrip.
Defence Minister Delfin Lorenzana had been scheduled to inspect an outpost on Thitu, one of the disputed Spratly Islands, but his trip was cancelled because of "safety issues" and he spent the day instead at a military base where he unveiled the development plans.
"We will build a runway and a port, a pier, for our ships" on Thitu, Lorenzana told troops at the Western Command's 41st anniversary. "We are a bit blind in that area."
Thitu is close to Subi Reef, one of seven manmade islands in the Spratlys that China is accused of militarising with surface-to-air missiles and other armaments.
The Philippines has squabbled with China for years over the South China Sea, but relations appear to have improved under President Rodrigo Duterte, who was scheduled to meet Chinese Vice Premier Wang Yang in Davao City in the southern Philippines on Friday.
The minister said Duterte had given approval to upgrade facilities not only on Thitu but on the eight other features in the South China Sea it occupies.
Defence ministry spokesman Arsenio Andolong said landing on a porous runway on Thitu after heavy rains would have been dangerous.
A senior Philippine general said, however, the military also blocked a planned trip by a group of lawmakers to Thitu on Thursday, more because of concern over how China would react.
"That is a contested area, that is not 100 percent ours," Lieutenant-General Raul del Rosario told a Congressional hearing on Thursday.
"That's why we are concerned if you fly there. Every time an aircraft flies there, it gets a warning and there are times they fire flares towards the aircraft."
The military declined to comment on Rosario's statement.
A fishing community of about 110 people live on Thitu. China has troops on islands it occupies but not civilians.
China claims most of the South China Sea, a strategic waterway through which about $5 trillion of goods passes each year. Brunei, Malaysia, the Philippines, Taiwan and Vietnam also have claims. (Reporting by Manuel Mogato; Editing by Andrew Roche)