The storm, packing maximum sustained winds of 193 kph made landfall south-southwest of Marquelia in the state of Guerrero, at about 9:15pm Central Standard Time, the US National Hurricane Center (NHC) said in a statement.
Although slow-moving it had strengthened rapidly during the day, and president Andres Manuel Lopez Obrador urged coastal dwellers to seek higher ground as the top disaster agency called a red alert in parts of Guerrero and neighbouring Oaxaca state.
“Don’t forget that life is the most important thing – material things can be replaced,” the president wrote on social media.
The storm could bring “extraordinary” rainfall to parts of Guerrero and Oaxaca, in excess of 250mm, said national water commission Conagua, which forecast more than 150mm to drench the southernmost state of Chiapas.
The Miami-based hurricane centre warned that the storm could bring life-threatening storm surges and flash flooding before moving inland over southern Mexico on Tuesday and weakening rapidly over the region’s high terrain.
In the typically laid-back surfer getaway of Puerto Escondido, Oaxaca, residents hurried on Monday to tow in boats and put away beach chairs.
“We’re very concerned,” said restaurant owner Paula Sanchez, adding that hurricanes in the area had become stronger in recent years.
Education officials ordered schools to close in parts of Oaxaca and Guerrero as the storm neared, and state power firm CFE said it was moving worker convoys to Oaxaca ahead of John’s arrival.
A hurricane warning has been declared for areas from the famous beach resort of Acapulco, which is still recovering from last year’s Hurricane Otis, to as far east as the Oaxacan tourist hub of Huatulco.
A tropical storm warning covered areas further east from Huatulco to the major port of Salina Cruz, home of Mexican state-run oil company Pemex’s Plargest domestic refinery.
The NHC warned that heavy rainfall from John may cause “significant and possibly catastrophic, life-threatening flash flooding and mudslides,” in the states of Chiapas, Oaxaca and southeast Guerrero through Thursday.