As Malaysian government vessels continued to remain in Singapore's territorial waters off Tuas, several MPs have taken to social media to explain the situation to residents.

Marsiling-Yew Tee GRC MP Alex Yam went a step further. Late on Friday night, he posted on his Facebook page an image that transposed a map of the maritime boundary lines in the area onto another map that shows the position of vessels based on their automatic identification system (AIS) tracker.

The AIS is intended to allow ships to view marine traffic in their area and to be seen by other ships.

And the image Mr Yam, who is executive director of the People's Action Party (PAP) headquarters, posted showed Malaysian Marine Department vessel MV Polaris squarely within Singapore territorial waters as at 11.55pm on Friday.

"It lies only approximately 0.5 nautical mile off the shore of Tuas based on a straight-line waypoint plot from the vessel to the edge of our port," Mr Yam wrote in his post.

"By plotting in the approximate positions of the 1995 Bilateral Territorial Waters boundary, the 1979 arbitrary claim by Malaysia, the 1999 Johor Port Limits and the 2018 Singapore Port Limits (not to scale), it is obvious that the MV Polaris is not only outside its own Johor port limits and the 1979 claim by Malaysia but intruding into our maritime boundary," he added.

"It has done so for the last few days, despite warnings by our patrol vessels of its violations. It is also not the only vessel, there are two others moored within our boundary, and a total of 14 intrusions since late November 2018, a blatant provocation."

Singapore and Malaysia agreed on most of their maritime boundary along the Johor Strait in a 1995 agreement. But the Republic did not accept Malaysia's claims in a 1979 map, which also covered areas outside the 1995 agreement.

On Oct 25, Malaysia gazetted altered port limits that went beyond its past claims. Singapore has protested against the claim, which it surfaced last Tuesday. The Republic also extended its port limits off Tuas to the full extent of its territorial waters on Thursday.

Malaysia in turn sent a diplomatic note on Friday objecting to that move, and asking both countries to cease and desist from sending assets into the disputed area - a point its Foreign Minister Saifuddin Abdullah also made in a statement.

Mr Yam described this call as "incredulous". "In asking both countries to leave the area it means that by having intruded into our waters, they would now have us removed from our own waters," he wrote.

"Their vessels undertook what are deemed as unauthorised, unlawful activities under international law within our territorial waters and yet want us out," he added.

Said Mr Yam: "We are reasonable people and are not raring for a fight, but as articulated plainly by Defence Minister Dr Ng Eng Hen: 'Singaporeans are peace-loving, but I strongly caution violators to leave Singapore territorial waters'."

Shortly before Mr Yam's post, Singapore's Ministry of Foreign Affairs (MFA) issued a statement categorically rejecting Malaysia's proposal and asking its vessels to leave.

Former MFA permanent secretary Bilahari Kausikan also wrote on Facebook: "You have to admire the Malaysian Foreign Minister's chutzpah: you create a problem; when we respond to defend our interests, you say that the solution to the problem you created in the first place is for us to cease defending our interests and to accept equal responsibility for the problem!

"Sorry, bro. Good try but no cigar. We are not daft," he added.